Leetcode 256. Paint House

[locked]

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.

Using DP. Try 3 paint ways and get the min.

# Time:  O(n)
# Space: O(1)

class Solution(object):
    def minCost(self, costs):
        """
        :type costs: List[List[int]]
        :rtype: int
        """
        if not costs:
            return 0
        
        min_cost = [costs[0], [0, 0, 0]]
        
        n = len(costs)
        for i in xrange(1, n):
            min_cost[i % 2][0] = costs[i][0] + \
                                 min(min_cost[(i - 1) % 2][1], min_cost[(i - 1) % 2][2])
            min_cost[i % 2][1] = costs[i][1] + \
                                 min(min_cost[(i - 1) % 2][0], min_cost[(i - 1) % 2][2])
            min_cost[i % 2][2] = costs[i][2] + \
                                 min(min_cost[(i - 1) % 2][0], min_cost[(i - 1) % 2][1])

        return min(min_cost[(n - 1) % 2])