README_EN.md

17.14. Smallest K

中文文档

Description

Design an algorithm to find the smallest K numbers in an array.

Example:

Input:  arr = [1,3,5,7,2,4,6,8], k = 4
Output:  [1,2,3,4]

Note:

• 0 <= len(arr) <= 100000
• 0 <= k <= min(100000, len(arr))

Solutions

Python3

class Solution:
    def smallestK(self, arr: List[int], k: int) -> List[int]:
        return sorted(arr)[:k]

class Solution:
    def smallestK(self, arr: List[int], k: int) -> List[int]:
        h = []
        for v in arr:
            heappush(h, -v)
            if len(h) > k:
                heappop(h)
        return [-v for v in h]

Java

class Solution {
    public int[] smallestK(int[] arr, int k) {
        Arrays.sort(arr);
        int[] ans = new int[k];
        for (int i = 0; i < k; ++i) {
            ans[i] = arr[i];
        }
        return ans;
    }
}

class Solution {
    public int[] smallestK(int[] arr, int k) {
        PriorityQueue<Integer> q = new PriorityQueue<>((a, b) -> b - a);
        for (int v : arr) {
            q.offer(v);
            if (q.size() > k) {
                q.poll();
            }
        }
        int[] ans = new int[k];
        int i = 0;
        while (!q.isEmpty()) {
            ans[i++] = q.poll();
        }
        return ans;
    }
}

C++

class Solution {
public:
    vector<int> smallestK(vector<int>& arr, int k) {
        sort(arr.begin(), arr.end());
        vector<int> ans(k);
        for (int i = 0; i < k; ++i) {
            ans[i] = arr[i];
        }
        return ans;
    }
};

class Solution {
public:
    vector<int> smallestK(vector<int>& arr, int k) {
        priority_queue<int> q;
        for (int& v : arr) {
            q.push(v);
            if (q.size() > k) {
                q.pop();
            }
        }
        vector<int> ans;
        while (q.size()) {
            ans.push_back(q.top());
            q.pop();
        }
        return ans;
    }
};

Go

func smallestK(arr []int, k int) []int {
	sort.Ints(arr)
	ans := make([]int, k)
	for i, v := range arr[:k] {
		ans[i] = v
	}
	return ans
}

func smallestK(arr []int, k int) []int {
	q := hp{}
	for _, v := range arr {
		heap.Push(&q, v)
		if q.Len() > k {
			heap.Pop(&q)
		}
	}
	ans := make([]int, k)
	for i := range ans {
		ans[i] = heap.Pop(&q).(int)
	}
	return ans
}

type hp struct{ sort.IntSlice }

func (h hp) Less(i, j int) bool  { return h.IntSlice[i] > h.IntSlice[j] }
func (h *hp) Push(v interface{}) { h.IntSlice = append(h.IntSlice, v.(int)) }
func (h *hp) Pop() interface{} {
	a := h.IntSlice
	v := a[len(a)-1]
	h.IntSlice = a[:len(a)-1]
	return v
}

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