【leetcode】1090. Largest Values From Labels

题目如下：

We have a set of items: the i-th item has value values[i] and label labels[i].

Then, we choose a subset S of these items, such that:

• |S| <= num_wanted
• For every label L, the number of items in Swith label L is <= use_limit.

Return the largest possible sum of the subset S.

 

Example 1:

Input: values = [5,4,3,2,1], labels = [1,1,2,2,3], num_wanted = 3, use_limit = 1
Output: 9
Explanation: The subset chosen is the first, third, and fifth item.

Example 2:

Input: values = [5,4,3,2,1], labels = [1,3,3,3,2], num_wanted = 3, use_limit = 2
Output: 12
Explanation: The subset chosen is the first, second, and third item.

Example 3:

Input: values = [9,8,8,7,6], labels = [0,0,0,1,1], num_wanted = 3, use_limit = 1
Output: 16
Explanation: The subset chosen is the first and fourth item.

Example 4:

Input: values = [9,8,8,7,6], labels = [0,0,0,1,1], num_wanted = 3, use_limit = 2
Output: 24
Explanation: The subset chosen is the first, second, and fourth item.

 

Note:

1. 1 <= values.length == labels.length <= 20000
2. 0 <= values[i], labels[i] <= 20000
3. 1 <= num_wanted, use_limit <= values.length

解题思路：贪心算法。每次取values中的最大值，如果对应labels没有超过限制，那么表示最大值可取；否则继续判断次大值。

代码如下：

class Solution(object):
    def largestValsFromLabels(self, values, labels, num_wanted, use_limit):
        """
        :type values: List[int]
        :type labels: List[int]
        :type num_wanted: int
        :type use_limit: int
        :rtype: int
        """
        res = 0
        def cmpf(v1,v2):
            if v1[0] - v2[0] != 0:
                return v2[0] - v1[0]
            return v2[1] - v1[1]
        val_list = sorted(zip(values,labels),cmp=cmpf)

        dic = {}
        inx = 0
        while num_wanted > 0 and inx < len(val_list):
            v,l = val_list[inx]
            if l not in dic or dic[l] < use_limit:
                res += v
                dic[l] = dic.setdefault(l,0) + 1
                num_wanted -= 1
            inx += 1
        return res