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
        //定义一个dp[i][j]表示前i个字符串和前j个字符串的最长公共子串
        int len1 = str1.length();
        int len2 = str2.length();
        int[][]dp = new int[len1 + 1][len2 + 1];
        int res = 0;
        //初始话数组
        for (int i = 0; i < len1; i++) {
            dp[i][0] = 0;
        }
        for (int i = 0; i < len2; i++) {
            dp[0][i] = 0;
        }
        for (int i = 1; i <= len1; i++) {
            for (int j = 1; j <= len2; j++) {
                if (str1.charAt(i-1) == str2.charAt(j-1)) {
                    dp[i][j] = dp[i - 1][j - 1] + 1;
                    res = Math.max(res, dp[i][j]);
                } else {
                    dp[i][j] = 0;
                }
            }
        }
        
        int index=0;
        for (int i = 1; i <= len1; i++) {
            for (int j = 1; j <= len2; j++) {
               if(dp[i][j]==res){
                    index=i;
                    break;
               }
            }
        }
        //a,b,c,d,e
        //0,1,2,3,4
        String r=str1.substring(index-res,index);
        return r;
    }
}