Leetcode 97, Interleaving String

    public boolean isInterleave(String s1, String s2, String s3) {
       if(s3.length() != s1.length() + s2.length()) {
            return false;    
       }
        
       int m = s1.length();
       int n = s2.length();
       boolean [][] dp = new boolean [m+1][n+1];
       dp[0][0]=true;
       
       for(int i = 1; i<=m; i++){
           if(s1.charAt(i-1)==s3.charAt(i-1)){
                dp[i][0] = dp[i-1][0];
           }
       }
       
       for(int i = 1; i<=n; i++){
           if(s2.charAt(i-1)==s3.charAt(i-1)){
                dp[0][i]=true;
           }
       }
       
       for(int i = 1; i <= m; i++){
           for(int j = 1; j <= n; j++){
               char c = s3.charAt(i+j-1);
               if(c == s1.charAt(i-1)){
                   if(dp[i-1][j]){
                        dp[i][j] = true;
                   }
               }
               if(c == s2.charAt(j-1)){
                   if(dp[i][j-1]){
                        dp[i][j] = true;
                   }
               }
           }
       }
       
        return dp[m][n];
    }