97-Interleaving-String.java

class Solution {

    public boolean isInterleave(String s1, String s2, String s3) {
        if (s1.length() + s2.length() != s3.length()) {
            return false;
        }

        boolean[][] dp = new boolean[s1.length() + 1][s2.length() + 1];
        dp[s1.length()][s2.length()] = true;

        for (int i = dp.length - 1; i >= 0; i--) for (
            int j = dp[0].length - 1;
            j >= 0;
            j--
        ) {
            if (
                i < s1.length() &&
                s1.charAt(i) == s3.charAt(i + j) &&
                dp[i + 1][j]
            ) {
                dp[i][j] = true;
            }
            if (
                j < s2.length() &&
                s2.charAt(j) == s3.charAt(i + j) &&
                dp[i][j + 1]
            ) {
                dp[i][j] = true;
            }
        }

        return dp[0][0];
    }
}