leetcode 347. Top K Frequent Elements

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347. Top K Frequent Elements

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Total Accepted: 1246 Total Submissions: 2777 Difficulty: Medium

Given a non-empty array of integers, return the k most frequent elements.

For example,
Given [1,1,1,2,2,3] and k = 2, return [1,2].

Note: 

• You may assume k is always valid, 1 ≤ k ≤ number of unique elements.
• Your algorithm's time complexity must be better than O(n log n), where n is the array's size.

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题意：

找出数组中出现次数最多的k个元素

 

题解：

用map统计每个元素出现的个数

然后用 优先队列 或 排序 取出 前k个

 

20 / 20 test cases passed.	Status:  Accepted
Runtime: 56 ms

 

struct PP
{
    int val;
    int count;
}te;

bool cmp(PP a,PP b)
{
    return a.count > b.count;
}

class Solution {
public:
    vector<int> topKFrequent(vector<int>& nums, int k) {
        int n = nums.size();
        vector<int> ans;
        vector<PP> temp;
        map<int,int> mp;
        int i;
        for(i = 0;i < n;i++){
            mp[ nums[i] ]++;
        }
        for(map<int,int>::iterator it = mp.begin();it != mp.end();it++){
            te.val = it -> first;
            te.count = it -> second;
            temp.push_back(te);
        }
        sort(temp.begin(),temp.end(),cmp);
        for(i = 0;i < k;i++){
            ans.push_back(temp[i].val);
        }
        return ans;
    }
};