97. Interleaving String

Description

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

DP

唯一需要注意的就是不要越界啊。

class Solution {
    public boolean isInterleave(String s1, String s2, String s3) {
        if (s1 == null || s2 == null || s3 == null) {
            return false;
        }

        int m = s1.length();
        int n = s2.length();
        if (m + n != s3.length()) {
            return false;
        }
        
        // dp[i][j] means s1.substring(i) and s2.substring(j)
        boolean[][] dp = new boolean[m + 1][n + 1];
        for (int i = m; i >= 0; --i) {
            for (int j = n; j >= 0; --j) {
                if (i == m && j == n) {
                    dp[i][j] = true;
                } else if (i == m) {
                    dp[i][j] = dp[i][j + 1] && s2.charAt(j) == s3.charAt(i + j);
                } else if (j == n) {
                    dp[i][j] = dp[i + 1][j] && s1.charAt(i) == s3.charAt(i + j);
                } else {
                    dp[i][j] = (dp[i + 1][j] && s1.charAt(i) == s3.charAt(i + j))
                        || (dp[i][j + 1] && s2.charAt(j) == s3.charAt(i + j));
                }
            }
        }
        return dp[0][0];
    }
}