快排

public class QuikSort {

    public static void quick(int[] arr, int begin, int end) {
        //防止无限递归
        if (begin >= end) {
            return;
        }

        int key = arr[begin];
        int keyIndex = begin;

        for (int i = begin + 1; i < end; i++) {
            if (arr[i] < key) {
                //交换一次  keyIndex就要往后移动一位
                keyIndex++;

                //交换i位置值和keyIndex位置值
                int tmp = arr[keyIndex];
                arr[keyIndex] = arr[i];
                arr[i] = tmp;
            }
        }
        //无小于key位置值后，则交换key和keyIndex值
        arr[begin] = arr[keyIndex];
        arr[keyIndex] = key;

        //切分，递归
        quick(arr, begin, keyIndex);
        quick(arr, keyIndex + 1, end);

    }


    public static void main(String[] args) {
        int[] arr = new int[7];

        arr[0] = 7;
        arr[1] = 9;
        arr[2] = 18;
        arr[3] = 6;
        arr[4] = 4;
        arr[5] = 8;
        arr[6] = 10;

        quick(arr, 0, arr.length);

        for (int tmp : arr) {
            System.out.println(tmp + " ");
        }

    }
}