[main] Added longest substring problem

Author: cthacker-udel

pythonProblems/dp/lcs.py

@@ -15,11 +15,68 @@ def lcs(substr1: str, substr2: str) -> int:
         return 1 + lcs(substr1[:-1], substr2[:-1])
     return 0
 
+def print_lcs(substr1: str, substr2: str) -> str:
+    table = []
+    # initialize table
+    for _ in substr1 + " ":
+        table_row = []
+        for __ in substr2 + " ":
+            table_row.append(0)
+        table.append(table_row)
+        table_row = []
+
+    for i in range(1, len(substr1) + 1):
+        for j in range(1, len(substr2) + 1):
+            if substr2[j - 1] == substr1[i - 1]: ## if both characters match
+                table[i][j] = table[i - 1][j - 1] + 1 ## characters match, set the diagonal cell to the curr value + 1
+            else:
+                table[i][j] = max(table[i - 1][j], table[i][j - 1]) ## either up or left in the lookup table
+    ## start at bottom right, and follow the path, taking a diagonal left with the letters are the same
+
+    startCol = len(table[len(table) - 1]) - 1
+    startRow = len(table) - 1
+
+    _substr1 = " " + substr1
+    _substr2 = " " + substr2
+    substr = ''
+    pprint(table)
+    while startCol != 0 and startRow != 0:
+        if _substr1[startRow] == _substr2[startCol]:
+            ## jump diagonal, add letter
+            substr += _substr1[startRow]
+            startRow -= 1
+            startCol -= 1
+        else:
+            ## evaluate left
+            left_ = -1
+            if startCol > 0:
+                left_ = table[startRow][startCol - 1]
+            ## evaluate top
+            top_ = -1
+            if startRow > 0:
+                top_ = table[startRow - 1][startCol]
+            
+            if left_ == top_:
+                startCol -= 1
+            if left_ != -1 and top_ != -1:
+                startRow -= 1 if top_ > left_ else 0
+                startCol -= 1 if left_ > top_ else 0
+            if left_ == -1:
+                ## move up
+                startRow -= 1
+            if top_ == -1:
+                startCol -= 1
+    return substr[::-1]
+
+
 
 if __name__ == '__main__':
     x = 'abcbdab'
     y = 'bdcaba'
     print(lcs(x, y))
+    x2 = 'xmjyauzadfsf'
+    y2 = 'mzjawxuwqrwe'
+    print(print_lcs(x2, y2))
 
 
 

pythonProblems/dp/longestSubstring.py

@@ -0,0 +1,50 @@
+from pprint import pprint
+
+def longestSubstring(substr1: str, substr2: str) -> str:
+    table = []
+    for _ in substr1:
+        table_row = []
+        for __ in substr2:
+            table_row.append(0)
+        table.append(table_row)
+        table_row = []
+    
+    for i in range(len(substr1)):
+        for j in range(len(substr2)):
+            if substr1[i] == substr2[j]:
+                if i == 0:
+                    table[i][j] = 1
+                elif j == 0:
+                    table[i][j] = 1
+                else:
+                    table[i][j] = table[i - 1][j - 1] + 1
+
+    coords = []
+    max_value = 0
+    for eachrow in table:
+        max_value = max(max_value, max(eachrow))
+    
+    for i in range(len(table)):
+        for j in range(len(table[i])):
+            if table[i][j] == max_value:
+                coords.append((i, j))
+
+    substrs = []
+    for eachcoord in coords:
+        x_ = eachcoord[1]
+        y_ = eachcoord[0]
+        substr = ''
+        while table[y_][x_] != 0 and x_ >= 0 and y_ >= 0:
+            substr += substr1[x_]
+            x_ -= 1
+            y_ -= 1
+        substrs.append(substr)
+    print(substrs)
+    
+    
+
+
+if __name__ == '__main__':
+    s1 = 'abab'
+    s2 = 'baba'
+    longestSubstring(s1, s2)