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title: 最小的 date: 2019-08-21T11:00:41+08:00 draft: false categories: offer

题目

牛客网

输入n个整数，找出其中最小的K个数。例如输入4,5,1,6,2,7,3,8这8个数字，则最小的4个数字是1,2,3,4,。

解题思路

1. 利用堆排序原理，计算出最小的 k 个数

public ArrayList<Integer> GetLeastNumbers_Solution(int[] input, int k) {
    ArrayList<Integer> res = new ArrayList<>();
    if (k > input.length || k == 0) {
        return res;
    }

    for (int i = input.length - 1; i >= 0; i--) {
        minHeap(input, 0, i);

        swap(input, 0, i);

        res.add(input[i]);
        if (res.size() == k) break;
    }
    return res;
}

private void minHeap(int[] heap, int start, int end) {
    if (start == end) {
        return;
    }

    int childLeft = start * 2 + 1;
    int childRight = childLeft + 1;

    if (childLeft <= end) {
        minHeap(heap, childLeft, end);

        if (heap[childLeft] < heap[start]) {
            swap(heap, start, childLeft);
        }
    }

    if (childRight <= end) {
        minHeap(heap, childRight, end);

        if (heap[childRight] < heap[start]) {
            swap(heap, start, childRight);
        }
    }
}

private void swap(int[] nums, int a, int b) {
    int t = nums[a];
    nums[a] = nums[b];
    nums[b] = t;
}