2744. Find Maximum Number of String Pairs

Problem

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.

Solution (Java)

class Solution {
    public int maximumNumberOfStringPairs(String[] words) {
      int ans = 0;
      for (int i = 0; i < words.length; i ++) {
          for(int j = i + 1; j < words.length; j ++)
              if(words[i].charAt(0) == words[j].charAt(1) && words[i].charAt(1) == words[j].charAt(0))
              ans ++;
      }
      return ans;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).