[LeetCode] 037: Interleaving String

[Problem]

Given s1, s2, s3, find whether s3 is formed by the interleaving of s1 and s2.

For example,
Given:
s1 = "aabcc",
s2 = "dbbca",

When s3 = "aadbbcbcac", return true.
When s3 = "aadbbbaccc", return false.

[Solution]

class Solution {
public:
    bool isInterleave(string s1, string s2, string s3) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function    

        // special cases
        int len1 = s1.size(), len2 = s2.size(), len3 = s3.size();
        if(len1 + len2 != len3)return false;
        if(len3 == 0)return true;
        
        // initial
        bool **dp = new bool*[len1+1];
        for(int i = 0; i <= len1; ++i){
            dp[i] = new bool[len2+1];
        }
        dp[len1][len2] = true;
        
        // set the last row except the last column
        for(int i = len2-1; i >= 0; --i){
            if(s2[i] == s3[len3-len2+i] && dp[len1][i+1]){
                dp[len1][i] = true;
            }
            else{
                dp[len1][i] = false;
            }
        }
        
        // set the last column except the last row
        for(int i = len1-1; i >= 0; --i){
            if(s1[i] == s3[len3-len1+i] && dp[i+1][len2]){
                dp[i][len2] = true;
            }
            else{
                dp[i][len2] = false;
            }
        }
        
        // dp
        for(int i = len1-1; i >= 0; --i){
            for(int j = len2-1; j >= 0; --j){
                if((s1[i] == s3[i+j] && dp[i+1][j]) || (s2[j] == s3[i+j] && dp[i][j+1])){
                    dp[i][j] = true;
                }
                else{
                    dp[i][j] = false;
                }
            }
        }
        return dp[0][0];
    }
};

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