SumOfEvenNumbersAfterQueries.cpp

// Source : https://leetcode.com/problems/sum-of-even-numbers-after-queries/
// Author : Hao Chen
// Date   : 2019-02-05

/***************************************************************************************************** 
 *
 * We have an array A of integers, and an array queries of queries.
 * 
 * For the i-th query val = queries[i][0], index = queries[i][1], we add val to A[index].  Then, the 
 * answer to the i-th query is the sum of the even values of A.
 * 
 * (Here, the given index = queries[i][1] is a 0-based index, and each query permanently modifies the 
 * array A.)
 * 
 * Return the answer to all queries.  Your answer array should have answer[i] as the answer to the 
 * i-th query.
 * 
 * Example 1:
 * 
 * Input: A = [1,2,3,4], queries = [[1,0],[-3,1],[-4,0],[2,3]]
 * Output: [8,6,2,4]
 * Explanation: 
 * At the beginning, the array is [1,2,3,4].
 * After adding 1 to A[0], the array is [2,2,3,4], and the sum of even values is 2 + 2 + 4 = 8.
 * After adding -3 to A[1], the array is [2,-1,3,4], and the sum of even values is 2 + 4 = 6.
 * After adding -4 to A[0], the array is [-2,-1,3,4], and the sum of even values is -2 + 4 = 2.
 * After adding 2 to A[3], the array is [-2,-1,3,6], and the sum of even values is -2 + 6 = 4.
 * 
 * Note:
 * 
 * 	1 <= A.length <= 10000
 * 	-10000 <= A[i] <= 10000
 * 	1 <= queries.length <= 10000
 * 	-10000 <= queries[i][0] <= 10000
 * 	0 <= queries[i][1] < A.length
 * 
 ******************************************************************************************************/
class Solution {
public:
    vector<int> sumEvenAfterQueries(vector<int>& A, vector<vector<int>>& queries) {
        int sum = 0;
        for(int i=0; i<A.size(); i++) {
            if (A[i] % 2 == 0) sum += A[i];
        }
        vector<int> result;
        for(auto query : queries) {
            int i = query[1];
            int x = A[i] + query[0];
            
            if (A[i] % 2 == 0 && x %2 == 0) {
                sum += ( -A[i] + x ); 
                A[i] = x;
            } else if (A[i] % 2 != 0 && x %2 == 0) {
                sum += x;
                A[i] = x;
            } else if (A[i] % 2 == 0 && x %2 != 0) {
                sum -= A[i];
                A[i] = x;
            } else if (A[i] % 2 != 0 && x %2 != 0){ 
                A[i] = x;
            }
            result.push_back(sum);
        }
        
        if (result.size()<=0) result.push_back(0);
        return result;
    }
};