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class Solution {
public:
    int minCostII(vector<vector<int>>& costs) {
        int k=costs[0].size(), n=costs.size(), firstMin, secondMin;

        for(int house=1; house<n; house++){
            firstMin = secondMin = -1;
            // Get the min and second min cost color in previous row.
            for(int color=0; color<k; color++){
                int cost = costs[house-1][color];
                if(firstMin == -1 || cost < costs[house-1][firstMin]){
                    secondMin = firstMin;
                    firstMin = color;
                }
                else if(secondMin == -1 || cost < costs[house-1][secondMin]){
                    secondMin = color;
                }
            }

            // Calculate the cumulative cost for current row.
            for(int color=0; color<k; color++){
                if(color == firstMin)
                    costs[house][color] += costs[house-1][secondMin];
                else
                    costs[house][color] += costs[house-1][firstMin];
            }
        }

        return *min_element(costs[n-1].begin(), costs[n-1].end());
    }
};