97. 交错字符串

class Solution {
public:
    bool isInterleave(string s1, string s2, string s3) {
        if(s1=="")
            return s2==s3;
        if(s2=="")
            return s1==s3;
        int n=s1.size();
        int m=s2.size();
        if(s3.size()!=(m+n))
            return false;
        vector<vector<int>> dp(n+1,vector<int>(m+1,0));
        for(int i=0;i<=n;i++){
            for(int j=0;j<=m;j++){
                if(i==0&&j==0){
                    dp[0][0]=1;
                }
                else if(i==0){
                    if(s3[j-1]==s2[j-1]&&dp[0][j-1]){
                        dp[0][j]=1;
                    }
                }
                else if(j==0){
                    if(s3[i-1]==s1[i-1]&&dp[i-1][0]){
                        dp[i][0]=1;
                    }
                }
                else{
                    if((s1[i-1]==s3[i+j-1]&&dp[i-1][j])||(s2[j-1]==s3[i+j-1]&&dp[i][j-1])){
                        dp[i][j]=1;
                    }
                }
            }
        }
        return dp[n][m];
    }
};