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LuoHong
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‎.gitignore

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# Compiled class file
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*.class
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*.DS_Store
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*/.DS_Store
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# Log file
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*.log

‎Code/Java/1.两数之和/TwoSum.java

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import java.util.HashMap;
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import java.util.Map;
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public class TwoSum {
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public static void main(String[] args) {
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// System.out.println("Hello World\n");
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TwoSum ts = new TwoSum();
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int[] nums = {2, 7, 11, 15};
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int[] result = ts.twoSum(nums, 9);
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for (int n: result) {
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System.out.println(n);
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}
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}
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public int[] twoSum(int[] nums, int target) {
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Map<Integer, Integer> map = new HashMap<>();
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for (int i = 0; i < nums.length; i++) {
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int temp = target - nums[i];
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if (map.containsKey(temp)) {
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return new int[] {map.get(temp), i};
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}
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map.put(nums[i], i);
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}
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return new int[0];
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}
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}

‎Code/Java/13.罗马数字转整数/RomanToInteger.java

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import java.util.HashMap;
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// import java.util.String;
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class RomanToInteger {
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public static void main(String[] args) {
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// System.out.println("Hello World\n");
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System.out.println(romanToInt("IV"));
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}
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public static int romanToInt(String s) {
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int sum = 0;
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if (s.indexOf("IV") != -1 || s.indexOf("IX") != -1) {
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sum -= 2;
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}
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if (s.indexOf("XL") != -1 || s.indexOf("XC") != -1) {
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sum -= 20;
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}
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if (s.indexOf("CD") != -1 || s.indexOf("CM") != -1) {
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sum -= 200;
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}
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for (int i = 0; i < s.length(); i++) {
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Character c = s.charAt(i);
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if (c == 'I') {
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sum += 1;
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} else if (c == 'V') {
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sum += 5;
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} else if (c == 'X') {
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sum += 10;
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} else if (c == 'L') {
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sum += 50;
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} else if (c == 'C') {
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sum += 100;
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} else if (c == 'D') {
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sum += 500;
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} else if (c == 'M') {
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sum += 1000;
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}
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}
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return sum;
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}
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/*
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字符 数值
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I 1 73
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V 5 86
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X 10 88
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L 50 76
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C 100 67
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D 500 68
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M 1000 77
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*/
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public static int romanToInt2(String s) {
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HashMap<Character, Integer> map = new HashMap<Character, Integer>();
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map.put('I', 1);
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map.put('V', 5);
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map.put('X', 10);
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map.put('L', 50);
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map.put('C', 100);
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map.put('D', 500);
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map.put('M', 1000);
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int sum = 0;
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int last = -1;
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for (int i = 0; i < s.length(); i++) {
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int num = map.get(s.charAt(s.length() - 1 - i));
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if (num < last) {
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System.out.println(num);
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sum -= num;
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} else {
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System.out.println(num);
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sum += num;
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}
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last = num;
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}
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return sum;
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}
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}

‎Code/Java/27.移除元素/RemoveElement.java

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public class RemoveElement {
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public static void main(String[] args) {
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int[] nums = {3,2,2,3};
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int val = 3;
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System.out.println(removeElement(nums, val));
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}
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public static int removeElement(int[] nums, int val) {
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int newLength = 0;
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for (int i = 0; i < nums.length; i ++) {
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if (nums[i] != val) {
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nums[newLength] = nums[i];
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newLength ++;
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}
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}
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return newLength;
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}
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}

‎Code/Java/283.移动零/MoveZeroes.java

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public class MoveZeroes {
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public static void main(String[] args) {
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int[] nums = {0,1,0,3,12};
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moveZeroes(nums);
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}
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public static void moveZeroes(int[] nums) {
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int length = nums.length;
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int fast = 0;
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int slow = 0;
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while (slow < length) {
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if (fast < length && nums[fast] != 0) {
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nums[slow] = nums[fast];
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slow++;
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}
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if (fast >= length) {
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nums[slow] = 0;
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slow++;
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}
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fast++;
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}
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for (int n : nums) {
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System.out.println(n);
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}
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}
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}

‎Code/Java/66.加一/PlusOne.java

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public class PlusOne {
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public static void main(String[] args) {
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int[] nums = {9};
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int[] digits = plusOne(nums);
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for (int n : digits) {
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System.out.println(n);
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}
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}
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public static int[] plusOne(int[] digits) {
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int idx = digits.length - 1;
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while (idx >= 0) {
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if (digits[idx] == 9) {
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digits[idx] = 0;
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} else {
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digits[idx] = digits[idx] + 1;
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break;
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}
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idx --;
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}
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if (digits[0] == 0) {
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digits = new int[digits.length + 1];
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digits[0] = 1;
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}
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return digits;
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}
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}

‎Code/Java/7.整数反转/reverseinteger.java

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public class reverseinteger
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{
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public static void main(String[] args)
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{
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// System.out.println("Hello World\n");
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System.out.println(reverse(214783647));
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System.out.println(Integer.MAX_VALUE);
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System.out.println(Integer.MIN_VALUE);
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}
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public static int reverse(int x) {
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int reverse = 0;
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while(x != 0) {
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int pop = x % 10;
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x /= 10;
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if (reverse > Integer.MAX_VALUE / 10 || (reverse == Integer.MAX_VALUE / 10 && pop > Integer.MAX_VALUE % 10)) {
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return 0;
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}
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if (reverse < Integer.MIN_VALUE / 10 || (reverse == Integer.MIN_VALUE / 10 && pop < Integer.MIN_VALUE % 10)) {
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return 0;
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}
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reverse = reverse * 10 + pop;
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}
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return reverse;
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}
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}

‎Code/Java/88.合并两个有序数组/MergeSortedArray.java

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public class MergeSortedArray {
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public static void main(String[] args) {
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int[] nums1 = new int[6];
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nums1[0] = 1;
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nums1[1] = 2;
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nums1[2] = 3;
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int[] nums2 = {1,2,3};
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merge(nums1, 3, nums2, 3);
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}
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public static void merge(int[] nums1, int m, int[] nums2, int n) {
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int j = m - 1;
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int k = n - 1;
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for (int i = nums1.length - 1; i >= 0; i --) {
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if (k >= 0 && j >= 0 && nums2[k] > nums1[j] ) {
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nums1[i] = nums2[k];
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k --;
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} else if (j >= 0) {
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nums1[i] = nums1[j];
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j --;
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} else if (k >= 0) {
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nums1[i] = nums2[k];
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k --;
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}
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}
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for (int n1 : nums1) {
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System.out.println(n1);
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}
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}
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}

‎Code/Java/9.回文数/palindromenumber.java

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public class palindromenumber {
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public static void main(String[] args)
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{
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// System.out.println("Hello World\n");
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System.out.println(isPalindrome(122221));
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}
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public static boolean isPalindrome(int x) {
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// 题干得 负数回文后 负号在后面，不成立
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// 如果最后一位0，第一位也应该为0. 所以排除，但是 如果 x = 0，例外。
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if (x < 0 || (x % 10 == 0 && x != 0)) {
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return false;
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}
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int revertedNumber = 0;
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while (x > revertedNumber) {
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revertedNumber = revertedNumber * 10 + x % 10;
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x /= 10;
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}
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// 如果 x 位数为奇数时，中间数反转后是不变的。所以可以直接忽略 x = revertedNumber / 10
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// 如果 x 位数为偶数时，revertedNumber = x 跳出循环。
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return x == revertedNumber || x == revertedNumber / 10;
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}
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}

‎README.md

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# Leetcode_Answer
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Leetcode 题解
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# Leetcode_Solution
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This is my Leetcode Solution note
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----------------
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[中文版](./README_ZH.md)
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| Title | Solution | Topic | Note | Difficulty |
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| ----- | -------- | ----- | ---- | ---------- |
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|[1.Two Sum](https://leetcode.com/problems/reverse-integer/) |[Java](./Code/Java/7.整数反转/reverseinteger.java)|`Array` `HashTable` `Math` | |Easy|
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|[7. Reverse Integer](https://leetcode.com/problems/reverse-integer/) |[Java](./Code/Java/7.整数反转/reverseinteger.java)|`Math` | |Easy|
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|[1.Two Sum](https://leetcode.com/problems/two-sum/) |[Java](./Code/Java/1.两数之和/TwoSum.java)|`Array` `HashTable` | |Easy|

‎README_ZH.md

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# 力扣解答
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这是我的力扣解答笔记
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----------------
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[英文版](./README.md)
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| 题目 | 解答 | 话题 | 笔记 | 难度 |
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| ----- | -------- | ----- | ---- | ---------- |
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|[](https://leetcode-cn.com/problems/two-sum/) | [Java](./Code/Java/)|`数组` `哈希表` `双指针` `字符串` `数学` | |Easy|
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|[7.整数反转](https://leetcode-cn.com/problems/reverse-integer/) | [Java](./Code/Java/7.整数反转/reverseinteger.java)| `数学` | |Easy|
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|[1. 两数之和](https://leetcode-cn.com/problems/two-sum/) | [Java](./Code/Java/1.两数之和/TwoSum.java)|`数组` `哈希表` | |Easy|

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