LeetCode

题目：

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.

思路：

1) 递归

2) 动态规划，仍然沿用递归时的判断条件

package dp;

import java.util.Arrays;

public class InterleavingString {

    public boolean isInterleave(String s1, String s2, String s3) {
        int len1 = s1.length();
        int len2 = s2.length();
        int len3 = s3.length();
        if (len3 != len1 + len2) return false;
        char[] c12 = (s1 + s2).toCharArray();
        Arrays.sort(c12);
        char[] c3 = s3.toCharArray();
        Arrays.sort(c3);
        if (!isEqual(c12, c3, len3)) return false;
        return interleave(s1, s2, s3, len1, len2, len3, 0, 0, 0);
    }
    
    private boolean interleave(String s1, String s2, String s3, int len1, int len2, int len3, int i, int j, int k) {
        if (i == len1 && j == len2 && k == len3) return true;
        boolean flag = false;
        if (i < len1 && s1.charAt(i) == s3.charAt(k))
            flag = flag || interleave(s1, s2, s3, len1, len2, len3, i + 1, j, k + 1);
        if (j < len2 && s2.charAt(j) == s3.charAt(k))
            flag = flag || interleave(s1, s2, s3, len1, len2, len3, i, j + 1, k + 1);
        return flag;
    }
    
    private boolean isEqual(char[] c0, char[] c1, int n) {
        for (int i = 0; i < n; ++i) {
            if (c0[i] != c1[i])
                return false;
        }
        return true;
    }
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        InterleavingString i = new InterleavingString();
        System.out.println(i.isInterleave("a", "b", "ab"));
        System.out.println(i.isInterleave("aabcc", "dbbca", "aadbbcbcac"));
        System.out.println(i.isInterleave("aabcc", "dbbca", "aadbbbaccc"));
    }

}

package dp;

import java.util.Arrays;

public class InterleavingString {

    public boolean isInterleave(String s1, String s2, String s3) {
        int len1 = s1.length();
        int len2 = s2.length();
        int len3 = s3.length();
        if (len3 != len1 + len2) return false;
        char[] c12 = (s1 + s2).toCharArray();
        Arrays.sort(c12);
        char[] c3 = s3.toCharArray();
        Arrays.sort(c3);
        if (!isEqual(c12, c3, len3)) return false;

        boolean[][] dp = new boolean[len1 + 1][len2 + 1];
        dp[0][0] = true;
        for (int i = 1; i <= len1; ++i) {
            dp[i][0] = (s1.charAt(i - 1) == s3.charAt(i - 1)) && dp[i - 1][0];
        }
        
        for (int i = 1; i <= len2; ++i) {
            dp[0][i] = (s2.charAt(i - 1) == s3.charAt(i - 1)) && dp[0][i - 1];
        }
        
        for (int i = 1; i <= len1; ++i) {
            for (int j = 1; j <= len2; ++j) {
                dp[i][j] = (s1.charAt(i - 1) == s3.charAt(i + j - 1) && dp[i - 1][j]) || 
                        (s2.charAt(j - 1) == s3.charAt(i + j - 1) && dp[i][j - 1]);
            }
        }
        
        return dp[len1][len2];
    }
    
    private boolean isEqual(char[] c0, char[] c1, int n) {
        for (int i = 0; i < n; ++i) {
            if (c0[i] != c1[i])
                return false;
        }
        return true;
    }
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        InterleavingString i = new InterleavingString();
        System.out.println(i.isInterleave("a", "b", "ab"));
        System.out.println(i.isInterleave("aabcc", "dbbca", "aadbbcbcac"));
        System.out.println(i.isInterleave("aabcc", "dbbca", "aadbbbaccc"));
    }

}