快速排序和二分查找(Java)

Posted 2020-12-03 飞晨信息

import java.util.Arrays;

public class Main {

    public static void main(String[] args) {

        int[] data = {2, 3, 5, 1, 4, 5, 2, 13, 51, 9, 10, 15, 17, 6, 21, 33, 44, 77, 22};

        System.out.println(Arrays.toString(data));
        quickSort(data, 0, data.length - 1);
        System.out.println(Arrays.toString(data));
        int index = binarySearch(data, 4);
        System.out.println(index);
    }

    private static int partition(int[] data, int left, int right) {
        int i = left;
        int j = right;
        //pivot
        int pivot = data[left + (right - left) / 2];
        //完成一趟排序
        while (i <= j) {
            //从右往左找到第一个小于pivot的数
            while (data[j] > pivot) {
                j--;
            }
            //从左往右找到第一个大于pivot的数
            while (data[i] < pivot) {
                i++;
            }
            //交换
            if (i <= j) {
                int p = data[i];
                data[i] = data[j];
                data[j] = p;
                i++;
                j--;
            }
        }

        return i;
    }

    public static void quickSort(int[] data, int left, int right) {

        int index = partition(data, left, right);

        if (left < index - 1) {
            quickSort(data, left, index - 1);
        }

        if (index < right) {
            quickSort(data, index, right);
        }
    }

    public static int binarySearch(int[] data, int target) {
        int left = 0, right = data.length - 1;
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (data[mid] < target) {
                left = mid + 1;
            }
            if (data[mid] >= target) {
                right = mid - 1;
            }
        }
        return left;
    }

    public int binarySearchRecur(int[] data, int target, int left, int right) {
        if (left > right) {
            return left;
        }
        int mid = left + (right - left) / 2;
        if (data[mid] < target) {
            return binarySearchRecur(data, target, mid + 1, right);
        } else {
            return binarySearchRecur(data, target, left, mid - 1);
        }
    }

}