2672. Number of Adjacent Elements With the Same Color

There is a 0-indexed array nums of length n. Initially, all elements are uncolored (has a value of 0).

You are given a 2D integer array queries where queries[i] = [indexi, colori].

For each query, you color the index indexi with the color colori in the array nums.

Return an array answer of the same length as queries where answer[i] is the number of adjacent elements with the same color after the ith query.

More formally, answer[i] is the number of indices j, such that 0 <= j < n - 1 and nums[j] == nums[j + 1] and nums[j] != 0 after the ith query.

class Solution {
public:
    vector<int> colorTheArray(int n, vector<vector<int>>& queries) {
        vector<int> C(n+2);
        vector<int> res;
        auto good = [&](int idx) {
            int res = 0;
            if(C[idx-1] and C[idx] and C[idx-1] == C[idx]) res += 1;
            if(C[idx+1] and C[idx] and C[idx+1] == C[idx]) res += 1;
            return res;
        };
        int now = 0;
        for(auto q : queries) {
            int idx = q[0] + 1, c = q[1];
            now -= good(idx);
            C[idx] = c;
            now += good(idx);
            res.push_back(now);
        }
        return res;
    }
};