lintcode:Paint House

Description
 Notes
 Testcase
 Judge
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.
Have you met this question in a real interview? 
Yes
 Notice
All costs are positive integers.
Example
Given  costs  =  [[14,2,11],[11,14,5],[14,3,10]]  return  10
house 0 is blue, house 1 is green, house 2 is blue,  2 + 5 + 3 = 10

class Solution {
public:
    /**
     * @param costs n x 3 cost matrix
     * @return an integer, the minimum cost to paint all houses
     */
    int minCost(vector>& costs) {
        // Write your code here
        if (costs.size() == 0) //          
            return 0;
        
        int n = costs.size();
        
        vector> dp(n, vector(3));
        
        //dp[i][j]       i  ，    j           
        
        for (int i=0; i<3; i++)
        {
            dp[0][i] = costs[0][i];
        }
        
        
        for (int i=1; i