交错字符串（dp）

题目：https://leetcode-cn.com/problems/interleaving-string/

class Solution {
public:
    bool isInterleave(string s1, string s2, string s3) {
        /*
        *给定三个字符串 s1, s2, s3, 验证 s3 是否是由 
        *s1 和 s2 交错组成的
        *dp[i][j]表示s1的前i个和s2的前j个能否构成s3的前i+j个
        */
        int len1 = s1.length();
        int len2 = s2.length();
        int len3 = s3.length();
        if(len1+len2 != len3) return false;
        int n = len1,m = len2;
        s1 = "#"+s1;
        s2 = "#"+s2;
        s3 = "#"+s3;
        vector dp;
        dp.resize(n+1);
        for(int i = 0;i