There are a row ofnhouses, each house can be painted with one of thekcolors. 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 anxkcost matrix. For example,costs[0][0]is the cost of painting house 0 with color 0;costs[1][2]is the cost of painting house 1 with color 2, and so on... Find the minimum cost to paint all houses.

Note: All costs are positive integers.

第i 个房子要选costs[i][ x ] 颜色成本最小的哪一个， 如果这个颜色与i-1 得到的结果颜色一直那么就不能选这个颜色， 继续找成本第二小的颜色。 这样一直算到最后一个。

min1   min2  当前第一小， 第二小。 

preMin1 preMin2 前一个第一小，第二小。