[LintCode] Problem 516 - Paint House II

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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.

Example

No.1

Input:
costs = [[14,2,11],[11,14,5],[14,3,10]]

Output: 10

Explanation:
The three house use color [1,2,1] for each house. The total cost is 10.

No.2

Input:
costs = [[5]]

Output: 5

Explanation:
There is only one color and one house.

Challenge

Could you solve it in O(nk)?

Code

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public int minCostII(int[][] costs) {
    int min1 = 0;
    int min2 = 0;
    int idx = 0;

    for (int i = 0; i < costs.length; i++) {
        int curMin1 = Integer.MAX_VALUE;
        int curMin2 = Integer.MAX_VALUE;
        int curIdx = 0;

        for (int j = 0; j < costs[i].length; j++) {
            int cost = costs[i][j] + (j == idx ? min2 : min1);

            if (cost < curMin1) {
                curMin2 = curMin1;
                curMin1 = cost;
                curIdx = j;
            }
            else if (cost < curMin2)
                curMin2 = cost;
        }

        min1 = curMin1;
        min2 = curMin2;
        idx = curIdx;
    }

    return min1;
}