256. Paint House

题目：

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.

Note:
All costs are positive integers.

链接： http://leetcode.com/problems/paint-house/

3/4/2017

感觉每次做dp的题目想法都是对的，但是每次总想建立数组来存之前的值，可能是受算法导论里面的影响。其实如果中间值只是在下一次循环时候用到的话，完全可以用几个变量来表示，变量的数目就是本来要用数组的数目。

还是借鉴别人的不用数组的写法

public class Solution {
    public int minCost(int[][] costs) {
        if (costs == null || costs.length == 0) return 0;
        
        int red = 0, blue = 0, green = 0;
        for (int i = 0; i < costs.length; i++) {
            int prevRed = red, prevBlue = blue, prevGreen = green;
            red = costs[i][0] + Math.min(prevBlue, prevGreen);
            blue = costs[i][1] + Math.min(prevRed, prevGreen);
            green = costs[i][2] + Math.min(prevBlue, prevRed);
        }
        return Math.min(red, Math.min(blue, green));
    }
}