1092-Shortest-Common-Supersequence.py

class Solution:
    def shortestCommonSupersequence(self, str1: str, str2: str) -> str:
        n, m = len(str1), len(str2)
        dp = [[0] * (m + 1) for _ in range(n + 1)]
        for i in range(1, n + 1):
            for j in range(1, m + 1):
                if str1[i-1] == str2[j - 1]:
                    dp[i][j] = dp[i - 1][j - 1] + 1
                else:
                    dp[i][j] = max(dp[i - 1][j], dp[i][j - 1])
        
        answer = ""
        i, j = n, m
        while i > 0 and j > 0:
            if str1[i - 1] == str2[j - 1]:
                answer += str1[i - 1]
                i, j = i - 1, j - 1
            elif dp[i - 1][j] > dp[i][j - 1]:
                answer += str1[i - 1]
                i = i - 1
            else:
                answer += str2[j - 1]
                j = j - 1
        answer = answer[::-1]
        return str1[0:i] + str2[0:j] + answer