冒泡排序和快速排序的java实现

转发请注明原创地址 http://www.cnblogs.com/dongxiao-yang/p/6264831.html

冒泡

    public static int[] bubble_sort(int[] arr) {
        int n = arr.length;
        for (int i = 0; i < n - 1; i++) {//每次循环代表一轮冒泡，一轮冒泡后顶端的数字一定是最大的
            for (int j = 0; j < n - 1 - i; j++) {
                if (arr[j] < (arr[j + 1])) {
                    int tmp = arr[j + 1];
                    arr[j + 1] = arr[j];
                    arr[j] = tmp;
                }

            }
        }

        return arr;

    }

快速排序1

    public static void quick_sort(int[] arr, int start, int end) {

        if (start >= end) {
            // System.out.println("qs finish");
            return;
        }
        int x = arr[start];
        int s = start;
        int e = end;

        while (s < e) {
            if (arr[e] < x) {
                for (; s < e; s++) {
                    if (arr[s] > x) {
                        int tmp = arr[s];
                        arr[s] = arr[e];
                        arr[e] = tmp;
                        // System.out.println("switch " + arr[s] + " " +
                        // arr[e]);
                        // System.out.println("s is " + s + " e is " + e);
                        break;
                    }
                }
            } else {
                e--;

            }
        }
        // System.out.println(" the end s is " + s + " e is " + e +
        // " arr[s] is "
        // + arr[s]+"  arr[start] is "+arr[start]);

        arr[start] = arr[s];

        arr[s] = x;


        System.out.println("quick_sort is "+Arrays.toString(arr));

        quick_sort(arr, start, s - 1);
        quick_sort(arr, s + 1, end);

    }

快速排序2代码优化

    public static void quick_sort2(int[] arr, int start, int end) {

        if (start < end) {

            int x = arr[start];
            int s = start;
            int e = end;

            while (s < e) { //退出循环代表一轮排序结束，首尾游标相遇
                while (s < e && (arr[e] >= x)) // 从右向左找第一个小于x的数
                {
                    e--;
                }

                while (s < e && (arr[s] <= x)) // 从右向左找第一个小于x的数
                {
                    s++;
                }

                if (s < e) {// 左右两个数交换
                    int tmp = arr[s];
                    arr[s] = arr[e];
                    arr[e] = tmp;

//                    System.out.println("switch " + arr[s] + " " + arr[e]);
//                    System.out.println("s is " + s + " e is " + e);
                }

            }

            arr[start] = arr[s]; //基准数归位到数组中正确位置

            arr[s] = x;

            System.out.println("quick_sort2 is "+Arrays.toString(arr));

            quick_sort2(arr, start, s - 1);
            quick_sort2(arr, s + 1, end);

        }

    }