Paint House II

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, costs0 is the cost of painting house 0 with color 0; costs1 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?

Still DP problem. The deduction is:
    costs[i][j] = unitCost[i][j] + Math.min(costs[i - 1][0, ..., k]) if j != the color that gets previous min.
    costs[i][j] = unitCost[i][j] + secondMin(costs[i - 1][0, ..., k]) if j == the color that gets previous min.

Track the min and second min for each iteration on j.

public int getCost(int[][] unitCost) {
        int n = unitCost.length;
        int k = unitCost[0].length;
        int[][] costs = new int[n][k];
        int prevMin = 0, prevSecond = 0;
        for (int i = 0; i < n; i++) {
            int currMin = Integer.MAX_VALUE, currSec = Integer.MAX_VALUE;
            for (int j = 0; j < k; j++) {
                if (i == 0) {
                    costs[i][j] = unitCost[i][j];
                } else {
                    costs[i][j] = prevMin == costs[i - 1][j] ? prevSecond : prevMin;
                }
                if (costs[i][j] < currMin) {
                    currSec = currMin;
                    currMin = costs[i][j];
                } else if (costs[i][j] < currSec) {
                    currSec = costs[i][j];
                }
            }
            prevMin = currMin;
            prevSecond = currSec;
        }
        return prevMin;
    }