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 an n x k cost matrix costs. 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... Return the minimum cost to paint all houses. Example 1: Input: costs = [[1,5,3],[2,9,4]] Output: 5 Explanation: Paint house 0 into color 0, paint house 1 into color 2. Minimum cost: 1 + 4 = 5; Or paint house 0 into color 2, paint house 1 into color 0. Minimum cost: 3 + 2 = 5. Example 2: Input: costs = [[1,3],[2,4]] Output: 5 Constraints: costs.length == n costs[i].length == k 1 <= n <= 100 1 <= k <= 20 1 <= costs[i][j] <= 20 Follow up: Could you solve it in O(nk) runtime?