Paint House II

Paint House II dynamic programming

There are a row of n houses, each house can be painted with one of the k colors. 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 k cost 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.

Follow up: Could you solve it in O(nk) runtime?

Paint House Ii Solution

public class PaintHouseII {
    public int minCostII(int[][] costs) {
        if(costs == null|| costs.length == 0) {
            return 0;
        }

        int m = costs.length;
        int n = costs[0].length;

        int min1 = -1;
        int min2 = -1;

        for(int i = 0; i < m; i++) {
            int last1 = min1;
            int last2 = min2;

            min1 = -1;
            min2 = -1;

            for(int j = 0; j < n; j++) {
                if(j != last1) {
                    costs[i][j] += last1 < 0 ? 0 : costs[i - 1][last1];
                } else {
                    costs[i][j] += last2 < 0 ? 0 : costs[i - 1][last2];
                }

                if(min1 < 0 || costs[i][j] < costs[i][min1]) {
                    min2 = min1;
                    min1 = j;
                } else if(min2 < 0 || costs[i][j] < costs[i][min2]) {
                    min2 = j;
                }
            }
        }

        return costs[m - 1][min1];
    }
}

Last modified October 4, 2020