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Commit 660ed84

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solve problem Top K Frequent Elements
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‎README.md

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|71|[Simplify Path](https://leetcode-cn.com/problems/simplify-path/description/)|[java/py/js](./algorithms/SimplifyPath)|Medium|
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|451|[Sort Characters By Frequency](https://leetcode-cn.com/problems/sort-characters-by-frequency/description/)|[java/py/js](./algorithms/SortCharactersByFrequency)|Medium|
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|215|[Kth Largest Element In An Array](https://leetcode-cn.com/problems/kth-largest-element-in-an-array/description/)|[java/py/js](./algorithms/KthLargestElementInAnArray)|Medium|
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|347|[Top K Frequent Elements](https://leetcode-cn.com/problems/top-k-frequent-elements/description/)|[java/py/js](./algorithms/TopKFrequentElements)|Medium|
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# Database
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|#|Title|Solution|Difficulty|
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# Top K Frequent Elements
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We can solve this problem by heap and hashmap
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class Solution {
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class Frequency {
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int value;
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int frequency;
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Frequency(int value, int frequency) {
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this.value = value;
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this.frequency = frequency;
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}
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}
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public List<Integer> topKFrequent(int[] nums, int k) {
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Map<Integer, Integer> frequencyMap = new HashMap<Integer, Integer>();
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for (int num : nums) {
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if (frequencyMap.get(num) == null)
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frequencyMap.put(num, 1);
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else
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frequencyMap.put(num, frequencyMap.get(num) + 1);
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}
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Comparator<Frequency> frequencyComparator = new Comparator<Frequency>() {
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public int compare(Frequency a, Frequency b) {
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return a.frequency > b.frequency ? -1 : (a.frequency == b.frequency ? 0 : 1);
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}
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};
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Queue<Frequency> queue = new PriorityQueue<Frequency>(frequencyComparator);
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for (int key : frequencyMap.keySet()) {
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queue.add(new Frequency(key, frequencyMap.get(key)));
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}
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List<Integer> res = new ArrayList<Integer>();
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for (int i = 0; i < k; i++)
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res.add(queue.poll().value);
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return res;
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}
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}
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/**
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* @param {number[]} nums
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* @param {number} k
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* @return {number[]}
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*/
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var topKFrequent = function(nums, k) {
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let frequencyMap = new Map()
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nums.forEach(num => {
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if (!frequencyMap.has(num))
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frequencyMap.set(num, 1)
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else
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frequencyMap.set(num, frequencyMap.get(num) + 1)
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})
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let maxHeap = new MaxHeap()
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for (let [key, value] of frequencyMap.entries())
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maxHeap.push(key, value)
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let res = []
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for (let i = 0; i < k; i++)
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res.push(maxHeap.pop())
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return res
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};
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function MaxHeap() {
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this.heap = []
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};
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MaxHeap.prototype.push = function(item, priority) {
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this.heap.push({item, priority})
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let pos = this.heap.length - 1,
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pPos = (pos % 2 == 0 ? pos - 2 : pos - 1) / 2
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while (pPos >= 0 && priority > this.heap[pPos].priority) {
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let temp = this.heap[pos]
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this.heap[pos] = this.heap[pPos]
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this.heap[pPos] = temp
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pos = pPos
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pPos = (pos % 2 == 0 ? pos - 2 : pos - 1) / 2
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}
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};
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MaxHeap.prototype.size = function() {
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return this.heap.length
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};
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MaxHeap.prototype.pop = function() {
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let size = this.size()
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if (size == 0)
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throw new Error('pop form empty list')
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else if (size == 1)
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return this.heap.pop().item
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let item = this.heap[0].item,
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pos = 0,
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maxChildPos = pos * 2 + 2
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this.heap[0] = this.heap.pop()
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if (maxChildPos < size - 1)
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maxChildPos = this.heap[maxChildPos].priority > this.heap[maxChildPos - 1].priority ? maxChildPos : maxChildPos - 1
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else
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maxChildPos = maxChildPos - 1 < size - 1 ? maxChildPos - 1 : pos
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while (maxChildPos < size - 1 && this.heap[pos].priority < this.heap[maxChildPos].priority) {
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let temp = this.heap[maxChildPos]
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this.heap[maxChildPos] = this.heap[pos]
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this.heap[pos] = temp
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pos = maxChildPos
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maxChildPos = pos * 2 + 2
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if (maxChildPos < size - 1)
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maxChildPos = this.heap[maxChildPos].priority > this.heap[maxChildPos - 1].priority ? maxChildPos : maxChildPos - 1
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else
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maxChildPos = maxChildPos - 1 < size - 1 ? maxChildPos - 1 : pos
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}
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return item
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};
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class Solution(object):
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def topKFrequent(self, nums, k):
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"""
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:type nums: List[int]
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:type k: int
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:rtype: List[int]
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"""
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frequency_map = {}
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for num in nums:
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if not frequency_map.get(num):
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frequency_map[num] = 1
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else:
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frequency_map[num] += 1
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heap = []
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for key, value in frequency_map.items():
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heap.append({ 'value': key, 'frequency': value })
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return [x['value'] for x in heapq.nlargest(k, heap, lambda e : e['frequency'])]
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