2399. Check Distances Between Same Letters

You are given a 0-indexed string s consisting of only lowercase English letters, where each letter in s appears exactly twice. You are also given a 0-indexed integer array distance of length 26.

Each letter in the alphabet is numbered from 0 to 25 (i.e. ‘a’ -> 0, ‘b’ -> 1, ‘c’ -> 2, … , ‘z’ -> 25).

In a well-spaced string, the number of letters between the two occurrences of the ith letter is distance[i]. If the ith letter does not appear in s, then distance[i] can be ignored.

Return true if s is a well-spaced string, otherwise return false.

class Solution {
public:
    bool checkDistances(string s, vector<int>& distance) {
        unordered_map<char,int> freq;
        for(int i = 0; i < s.length(); i++) {
            int idx = s[i] - 'a';
            if(freq.count(s[i])) {
                int dis = i - freq[s[i]] - 1;
                if(distance[idx] != dis) return false;
                distance[idx] = -1;
            } else freq[s[i]] = i;
        }
        for(auto& [k,_] : freq) {
            int idx = k - 'a';
            if(distance[idx] != -1) return false;
        }
        return true;
    }
};