You are given a?0-indexed?array?words?consisting of?distinct?strings.

The string?words[i]?can be paired with the string?words[j]?if:

• The string?words[i]?is equal to the reversed string of?words[j].

• 0 <= i < j < words.length.

Return?the?maximum?number of pairs that can be formed from the array?words.

Note that?each string can belong in?at most one?pair.

?

Example 1:

Input: words = ["cd","ac","dc","ca","zz"]Output: 2Explanation: In this example, we can form 2 pair of strings in the following way: - We pair the 0th string with the 2nd string, as the reversed string of word[0] is "dc" and is equal to words[2]. - We pair the 1st string with the 3rd string, as the reversed string of word[1] is "ca" and is equal to words[3]. It can be proven that 2 is the maximum number of pairs that can be formed.

Example 2:

Input: words = ["ab","ba","cc"]Output: 1Explanation: In this example, we can form 1 pair of strings in the following way: - We pair the 0th string with the 1st string, as the reversed string of words[1] is "ab" and is equal to words[0]. It can be proven that 1 is the maximum number of pairs that can be formed.

Example 3:

Input: words = ["aa","ab"]Output: 0Explanation: In this example, we are unable to form any pair of strings.

?

Constraints:

• 1 <= words.length <= 50

• words[i].length == 2

• words?consists of distinct strings.

• words[i]?contains only lowercase English letters.

找是否是反序的字符串對，用stringbuilder即可處理，

下面是代碼：

import java.util.Arrays;

public class Code2744 {

? ? public static void main(String[] args) {

? ? ? ?

? ? }

? ? public static int maximumNumberofStringPairs(String[]words){

? ? ? ? boolean[]bn=new boolean[words.length];

? ? ? ? int cnt=0;

? ? ? ? Arrays.fill(bn, false);

? ? ? ? for (int i = 0; i < words.length-1; i++) {

? ? ? ? ? ? for (int j = i+1; j < words.length; j++) {

? ? ? ? ? ? ? ? if(check(words[i], words[j])&&bn[i]==false&&bn[j]==false){

? ? ? ? ? ? ? ? ? ? bn[i]=true;

? ? ? ? ? ? ? ? ? ? bn[j]=true;

? ? ? ? ? ? ? ? ? ? cnt++;

? ? ? ? ? ? ? ? }

? ? ? ? ? ? }

? ? ? ? }

? ? ? ? return cnt;

? ? }

? ? public static boolean check(String a, String b){

? ? ? ? StringBuilder sb=new StringBuilder(a);

? ? ? ? if(sb.reverse().toString().equals(b)){

? ? ? ? ? ? return true;

? ? ? ? }else{

? ? ? ? ? ? return false;

? ? ? ? }

? ? }

}

Runtime:?8 ms, faster than?33.33%?of?Java?online submissions for?Find Maximum Number of String Pairs.

Memory Usage:?43.9 MB, less than?33.33%?of?Java?online submissions for?Find Maximum Number of String Pairs.