src/main/java/com/fishercoder/solutions/_265.java

package com.fishercoder.solutions;

public class _265 {

    public static class Solution1 {
        public int minCostII(int[][] costs) {
            if (costs == null || costs.length == 0) {
                return 0;
            }

            int n = costs.length;
            int k = costs[0].length;
            // min1 is the index of the 1st-smallest cost till previous house
            // min2 is the index of the 2nd-smallest cost till previous house
            int min1 = -1;
            int min2 = -1;

            for (int i = 0; i < n; i++) {
                int last1 = min1;
                int last2 = min2;
                min1 = -1;
                min2 = -1;

                for (int j = 0; j < k; j++) {
                    if (j != last1) {
                        // current color j is different to last min1
                        costs[i][j] += last1 < 0 ? 0 : costs[i - 1][last1];
                    } else {
                        costs[i][j] += last2 < 0 ? 0 : costs[i - 1][last2];
                    }

                    // find the indices of 1st and 2nd smallest cost of painting current house i
                    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[n - 1][min1];
        }
    }

}