# [LeetCode] 265. Paint House II 粉刷房子之二

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:

Input: [[1,5,3],[2,9,4]]
Output: 5
Explanation: Paint house 0 into color 0, paint house 1 into color 2. Minimum cost: 1 + 4 = 5;
Or paint house 0 into color 2, paint house 1 into color 0. Minimum cost: 3 + 2 = 5.


Could you solve it in O(nk) runtime?

class Solution {
public:
int minCostII(vector<vector<int>>& costs) {
if (costs.empty() || costs[0].empty()) return 0;
vector<vector<int>> dp = costs;
int min1 = -1, min2 = -1;
for (int i = 0; i < dp.size(); ++i) {
int last1 = min1, last2 = min2;
min1 = -1; min2 = -1;
for (int j = 0; j < dp[i].size(); ++j) {
if (j != last1) {
dp[i][j] += last1 < 0 ? 0 : dp[i - 1][last1];
} else {
dp[i][j] += last2 < 0 ? 0 : dp[i - 1][last2];
}
if (min1 < 0 || dp[i][j] < dp[i][min1]) {
min2 = min1; min1 = j;
} else if (min2 < 0 || dp[i][j] < dp[i][min2]) {
min2 = j;
}
}
}
return dp.back()[min1];
}
};

class Solution {
public:
int minCostII(vector<vector<int>>& costs) {
if (costs.empty() || costs[0].empty()) return 0;
int min1 = 0, min2 = 0, idx1 = -1;
for (int i = 0; i < costs.size(); ++i) {
int m1 = INT_MAX, m2 = m1, id1 = -1;
for (int j = 0; j < costs[i].size(); ++j) {
int cost = costs[i][j] + (j == idx1 ? min2 : min1);
if (cost < m1) {
m2 = m1; m1 = cost; id1 = j;
} else if (cost < m2) {
m2 = cost;
}
}
min1 = m1; min2 = m2; idx1 = id1;
}
return min1;
}
};

Github 同步地址：

https://github.com/grandyang/leetcode/issues/265

Product of Array Except Self

Sliding Window Maximum

Paint House

Paint Fence

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

https://leetcode.com/problems/paint-house-ii/discuss/69509/Easiest-O(1)-space-JAVA-solution

https://leetcode.com/problems/paint-house-ii/discuss/69492/AC-Java-solution-without-extra-space

https://leetcode.com/problems/paint-house-ii/discuss/69495/Fast-DP-Java-solution-Runtime-O(nk)-space-O(1)

LeetCode All in One 题目讲解汇总(持续更新中...)

posted @ 2016-03-26 14:26  Grandyang  阅读(15766)  评论(5编辑  收藏  举报