max-string-pairs.js

/*
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.


*/

var maximumNumberOfStringPairs = function(words) {
    let obj = {};
    let count = 0;

    for(let word of words) {

        let reverse = word[ 1 ] + word[ 0 ];

        if(obj[ reverse ] === true) count++;
        obj[ word ] = true;

    }
    return count;
};

// simple problem