[LeetCode256]Paint House

There are a row of n houses, each house can be painted with one of the three colors: red, blue or green. The cost of painting each house with a certain color is different. You have to paint all the houses such that no two adjacent houses have the same color.

The cost of painting each house with a certain color is represented by a n x 3 cost matrix. For example, costs[0][0] is the cost of painting house 0 with color red; costs[1][2] is the cost of painting house 1 with color green, and so on... Find the minimum cost to paint all houses.

All costs are positive integers.

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題目給的2d vector是costs。相鄰兩個house顏色只要不一樣就行了。這題只有三個顏色。所以對於每個current house i,如果把它刷成red, 則它是red的cost爲 cost[i][0] + min(lastG, lastB). lastG: 代表它前一個house爲green, lastB同理。

class Solution {
    int minCost(vector<vector<int>>& costs) {
        if(costs.empty()) return 0;
        int n = costs.size(), r = 0, g = 0, b = 0;
        for(int i = 0; i<n; ++i){
            int lastR = r, lastG = g, lastB = b;
            r = costs[i][0] + min(lastG, lastB);
            g = costs[i][1] + min(lastR, lastB);
            b = costs[i][2] + min(lastR, lastG);
        return min(r, min(g, b));
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