题解 | 最长公共子串

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 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
	    // i 从1开始；
        // dp[i][j] = dp[i-1][j-1] + 1 if str1[i-1] == str2[j-1] 
        // else dp[i][j] = 0
        int[][] dp = new int[str1.length()+1][str2.length()+1];
        int max = 0;
        int index = 0;
        for (int i =1;i <= str1.length();i++) {
            for(int j = 1;j <= str2.length();j++){
                if(str1.charAt(i-1) == str2.charAt(j-1)) {
                    dp[i][j] = dp[i-1][j-1] + 1;
                } else {
                    dp[i][j] = 0;
                }

                if(dp[i][j] > max) {
                    max= dp[i][j];
                    index = i;
                }
            }

        }   
        return str1.substring(index - max ,index);
    }
}