LeetCode--medium--interleaving_string_97

summary:

divide and conquer | memorization

package myapp.kit.leetcode.top200;

import java.util.HashMap;
import java.util.Map;

/**
 *
 * 97
 * hard
 * https://leetcode.com/problems/interleaving-string/
 *
 * Given s1, s2, s3, find whether s3 is formed by the interleaving of s1 and s2.
 *
 * Example 1:
 *
 * Input: s1 = "aabcc", s2 = "dbbca", s3 = "aadbbcbcac"
 * Output: true
 * Example 2:
 *
 * Input: s1 = "aabcc", s2 = "dbbca", s3 = "aadbbbaccc"
 * Output: false
 * @author huangdingsheng
 * @version 1.0, 2020/7/21
 */
public class interleaving_string_97 {

    private Map cache;

    public boolean isInterleave(String s1, String s2, String s3) {
        if (s1.length() + s2.length() != s3.length()) {
            return false;
        }
        cache = new HashMap<>();
        return search(s1, s2, s3);
    }

    // divide and conquer + memorization
    public boolean search(String s1, String s2, String s3) {
        String key = s1 + "-" + s2 + "-" + s3;
        if (cache.containsKey(key)) {
            return cache.get(key);
        }
        boolean result = false;
        if (s1.length() == 0) {
            result = s2.equals(s3);
        } else if (s2.length() == 0) {
            result = s1.equals(s3);
        } else {
            if (s1.charAt(s1.length() - 1) == s3.charAt(s3.length() - 1)) {
                result = result || search(s1.substring(0, s1.length() - 1), s2, s3.substring(0, s3.length() - 1));
            }
            // pruning
            if (!result) {
                if (s2.charAt(s2.length() - 1) == s3.charAt(s3.length() - 1)) {
                    result = result || search(s1, s2.substring(0, s2.length() - 1), s3.substring(0, s3.length() - 1));
                }
            }
        }
        cache.put(key, result);
        return result;
    }
}