#162 is completed

Author: Hamid Gasmi

5-string-processing-and-pattern-matching-algorithms/2-burrows-wheeler-suffix-arrays/bwtinverse.py

@@ -1,11 +1,54 @@
 # python3
 import sys
 
-def InverseBWT(bwt):
-    # write your code here
-    return ""
+class Burrows_Wheeler_Inverse:
 
+    def inverse(self, bwt_text):
+
+        last_column = [c for c in bwt_text]
+        first_column = [c for c in bwt_text]
+        first_column.sort()
+        last_to_first = self.build_last_to_first(first_column, last_column)
+
+        origin_text_list = []
+        origin_text_list.append(first_column[0])
+
+        i = 0
+        while last_to_first[i] != 0:
+            i = last_to_first[i]
+            origin_text_list.append(first_column[i])
+
+        origin_text_list.reverse()
+
+        return ''.join(origin_text_list)
+
+    def build_last_to_first(self, first_column, last_column):
+        last_to_first = []
+
+        first_occurence = dict()
+        for i in range(len(first_column)):
+            c = first_column[i]
+            if not c in first_occurence:
+                first_occurence[c] = i
+
+        char_count = dict()
+        for i in range(len(last_column)):
+            c = last_column[i]
+
+            if c in char_count:
+                count = char_count[c]
+                char_count[c] += 1
+            else:
+                char_count[c] = 1
+                count = 0
+
+            last_to_first.append(first_occurence[c] + count)
+        
+        return last_to_first
 
 if __name__ == '__main__':
     bwt = sys.stdin.readline().strip()
-    print(InverseBWT(bwt))
+    
+    bwt_inverse = Burrows_Wheeler_Inverse()
+
+    print(bwt_inverse.inverse(bwt))

5-string-processing-and-pattern-matching-algorithms/2-burrows-wheeler-suffix-arrays/bwtinverse_tests/03

@@ -1,4 +1 @@
-3
-ATAGA
-ATC
-GAT
+ATG$CAAA