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
        int len1= str1.length();
        int len2 = str2.length();
        int m=0,n=0,num=0;
        int[][] dp = new int[len1+1][len2+1];
        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;
                    if(num<dp[i][j]){
                        num=dp[i][j];
                        m=i;
                        n=j;
                    }
                }
                else
                    dp[i][j]=0;
            }
        }
        StringBuffer sb =new StringBuffer();
        while(dp[m][n]!=0){
            sb.append(str1.charAt(m-1));
            m--;
            n--;
        }
        if(sb.length()==0)
        return "-1";
        return sb.reverse().toString();
    }
}