题解 | #最长公共子串#

import java.util.*;


public class Solution {
    /**
     * longest common substring
     * @param str1 string字符串 the string
     * @param str2 string字符串 the string
     * @return string字符串
     */
    public String LCS (String str1, String str2) {
        // write code here
        if (str1 == null || str1.length() < 1 || str2 == null || str2.length() < 2) {
            return "";
        }
        char[] arr1 = str1.toCharArray();
        char[] arr2 = str2.toCharArray();
        int n = arr1.length;
        int m = arr2.length;
        int[][] dp = new int[n + 1][m + 1];
        int max = -1;
        int index = -1;
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= m; j++) {
                if (arr1[i - 1] == arr2[j - 1]) {
                    dp[i][j] = dp[i - 1][j - 1] + 1;
                }
                if (dp[i][j] > max) {
                    max = dp[i][j];
                    index = i - 1;
                }
            }
        }
        if (index > -1) {
            return str1.substring(index + 1 - max, index + 1);
        }
        return "";
    }
}