LeetCode2744. Find Maximum Number of String Pairs

一、题目

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: 2
Explanation: 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: 1
Explanation: 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: 0
Explanation: 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.

二、题解

class Solution {
public:
    int maximumNumberOfStringPairs(vector<string>& words) {
        int n = words.size();
        int res = 0;
        for(int i = 0;i < n;i++){
            for(int j = i + 1;j < n;j++){
                string s1 = words[i],s2 = words[j];
                if(s1[0] == s2[1] && s1[1] == s2[0]) res++;
            }
        }
        return res;
    }
};