排序

排序

package com.test;

public class Math {

    public static void main(String[] args) {
        int[] arr = { 1, 5, 2, 6, 9, 3 };
        int[] arr2 = { 1, 3, 6, 8, 9 };
        //sys(arr);
        System.out.println("-------------");
        // selectSort(arr);
        // sort(arr);
        int index = search_2(arr2, 9);
        System.out.println("index:" + index);
        // sys(arr);

    }

    // 打印
    public static void sys(int[] arr) {
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i]);
        }
        System.out.println();
    }

    // 快速排序
    public static void selectSort(int[] arr) {
        for (int i = 0; i < arr.length - 1; i++) {
            for (int j = i + 1; j < arr.length; j++) {
                if (arr[i] > arr[j]) {
                    int temp = arr[i];
                    arr[i] = arr[j];
                    arr[j] = temp;
                }
            }
        }
    }

    // 冒泡排序
    public static void sort(int[] arr) {
        for (int i = 0; i < arr.length - 1; i++) {
            /**
             * 相邻两个元素比较,每次外层循环结束后,可以确定最大值, 
             * 所以减i,去掉最后一个元素,减1是避免数组越界
             */
            for (int j = 0; j < arr.length - i - 1; j++) {
                if (arr[j] > arr[j + 1]) {
                    int temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                }
            }
        }
    }

    // 折半查找1(折半查找前提是:数组元素必须是有序的)
    public static int search_1(int[] arr, int key) {
        int min = 0;
        int max = arr.length - 1;
        int mid = (min + max) / 2;
        while (arr[mid] != key) {
            if (key > arr[mid])
                min = mid + 1;
            else
                max = mid - 1;
            if (min > max)
                return -1;
            mid = (min + max) / 2;
        }
        return mid;
    }

    // 折半查找2
    public static int search_2(int[] arr, int key) {
        int min = 0;
        int max = arr.length - 1;
        int mid = (max + min) >> 1;
        while (min <= max) {
            if (key > arr[mid])
                min = mid + 1;
            else if (key < arr[mid])
                max = mid - 1;
            else
                return mid;
            mid = (max + min) >> 1;
        }
        return -1;
    }
}