256. Paint House

https://leetcode.com/problems/paint-house/description/

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.

Note:
All costs are positive integers.

Sol :

public class Solution {
    public int minCost(int[][] costs) {
        
        // DP
        
        if (costs == null || costs.length == 0){
            return 0;
        }
        
        for (int i = 1; i < costs.length; i ++){
            // costs is an accumulative variable
            costs[i][0] += Math.min(costs[i-1][1], costs[i-1][2]);
            costs[i][1] += Math.min(costs[i-1][0], costs[i-1][2]);
            costs[i][2] += Math.min(costs[i-1][1], costs[i-1][0]);
            
        }
        
        int n = costs.length - 1;
        return Math.min(Math.min(costs[n][0], costs[n][1]), costs[n][2]);
        
    }
}