paintHouseII.java

    // 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?

public class Solution {

    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];       
        
    }

}