描述

給定兩個字串str1和str2,輸出兩個字串的最長公共子串 題目保證str1和str2的最長公共子串存在且唯一。    資料範圍： 1 \le |str1|,|str2| \le 50001≤∣str1∣,∣str2∣≤5000
要求： 空間複雜度 O(n^2)O(n2)，時間複雜度 O(n^2)O(n2)

示例1

輸入：

"1AB2345CD","12345EF"

返回值：

"2345"

    import java.util.*;

public class Solution {     /**      * longest common substring      * @param str1 string字串 the string      * @param str2 string字串 the string      * @return string字串      */     public String LCS (String str1, String str2) {         // write code here         int len1 = str1.length();         int len2 = str2.length();         String commonStr = "";         int commonLen = 0;         for(int i=0; i<len1; i++){             char temp = str1.charAt(i);             if(commonLen>(len1-i)){                 return commonStr;             }             for(int j=0; j<len2;j++){                 int tmpCommonLen = 0;                 String tmpCommonStr = "";                 int k1 = i;                 int k2 = j;                 while(k1<len1&&k2<len2&&str1.charAt(k1)==str2.charAt(k2)){                     tmpCommonLen ++;                     tmpCommonStr += str1.charAt(k1);                     k1++;                     k2++;                 }                 if(commonLen<tmpCommonLen){                     commonLen = tmpCommonLen;                     commonStr = tmpCommonStr;                 }             }                      }         return commonStr;     } }