算法排序之冒泡排序

冒泡排序

冒泡排序（bubble sort），以升序来说，最后的排列一定是从小到大的。冒泡就是从最低端（数组末尾）开始，相邻的两个元素交换，把小的值放在前面，第一次冒泡就把最小的元素放到最顶端（数组首位）。冒泡排序是交换排序

冒泡的逻辑

1.双层遍历
2.外循环i，比如i=0，就把最小值放到array[0]，即每次外循环结束后，都是第i个值（包含0哈）已经放好
3.内循环就是从末尾到i的交换，因为内循环位置肯定是大于等于0，最后一个元素总是j-1,而且j-1最终落到位置i上，因此j>i是一个条件

优缺点

最坏的情况就是升序或者降序排列，做降序或者升序的处理，判断与交换的总次数达到N的平方数
最好的情况也就是正序，外循环1次，内循环n次

最常见的冒泡例子

package com.java.arlgorithm.sort;

import lombok.extern.slf4j.Slf4j;

import java.util.Arrays;

/**
 * @author
 */
@Slf4j
public class BubbleSortTest {
    public static void main(String[] args) {
        int[] array = new int[]{5, 6, 4, 3, 1, 6};
        //printAll(array);
        bubbleSort(array);
        //printAll(array);
    }

    public static void bubbleSort(int[] array) {
        if (array == null || array.length == 0) {
            throw new NullPointerException();
        }
        int len = array.length;
        for (int i = 0; i < len; i++) {
            int tmp;
            for (int j = len - 1; j > i; j--) {
                if (array[j] < array[j - 1]) {
/*                    tmp = array[j];
                    array[j] = array[j - 1];
                    array[j - 1] = tmp;*/
                    swap(array, j, j - 1);
                }
                printAll(array);
            }
        }
    }

    /*    形式参数的交换无法使得真实参数交换
    public static void swap(int src, int des) {
            int tmp = 0;
            tmp = src;
            src = des;
            des = tmp;
        }*/
    public static void swap(int[] array, int src, int des) {
        int tmp;
        tmp = array[src];
        array[src] = array[des];
        array[des] = tmp;
    }

    public static void printAll(int[] array) {
        log.info(Arrays.toString(array));
    }
}

结果

2019-08-19 19:51:10,521   [main] INFO  BubbleSortTest  - [5, 6, 4, 3, 1, 6]
2019-08-19 19:51:10,523   [main] INFO  BubbleSortTest  - [5, 6, 4, 1, 3, 6]
2019-08-19 19:51:10,523   [main] INFO  BubbleSortTest  - [5, 6, 1, 4, 3, 6]
2019-08-19 19:51:10,523   [main] INFO  BubbleSortTest  - [5, 1, 6, 4, 3, 6]
2019-08-19 19:51:10,523   [main] INFO  BubbleSortTest  - [1, 5, 6, 4, 3, 6]
2019-08-19 19:51:10,523   [main] INFO  BubbleSortTest  - [1, 5, 6, 4, 3, 6]
2019-08-19 19:51:10,523   [main] INFO  BubbleSortTest  - [1, 5, 6, 3, 4, 6]
2019-08-19 19:51:10,523   [main] INFO  BubbleSortTest  - [1, 5, 3, 6, 4, 6]
2019-08-19 19:51:10,523   [main] INFO  BubbleSortTest  - [1, 3, 5, 6, 4, 6]
2019-08-19 19:51:10,523   [main] INFO  BubbleSortTest  - [1, 3, 5, 6, 4, 6]
2019-08-19 19:51:10,523   [main] INFO  BubbleSortTest  - [1, 3, 5, 4, 6, 6]
2019-08-19 19:51:10,523   [main] INFO  BubbleSortTest  - [1, 3, 4, 5, 6, 6]
2019-08-19 19:51:10,524   [main] INFO  BubbleSortTest  - [1, 3, 4, 5, 6, 6]
2019-08-19 19:51:10,524   [main] INFO  BubbleSortTest  - [1, 3, 4, 5, 6, 6]
2019-08-19 19:51:10,524   [main] INFO  BubbleSortTest  - [1, 3, 4, 5, 6, 6]

Process finished with exit code 0

冒泡优化

package com.java.arlgorithm.sort;

import lombok.extern.slf4j.Slf4j;

import java.util.Arrays;

/**
 * @author
 */
@Slf4j
public class BubbleSortTest {
    public static void main(String[] args) {
        int[] array = new int[]{5, 6, 4, 3, 1, 6};
        int[] arrayOptmize = new int[]{1, 2, 3, 4, 5, 6};
        //printAll(array);
        //bubbleSort(array);
        bubbleSortOptmize(arrayOptmize);
        //printAll(array);
    }

    public static void bubbleSort(int[] array) {
        if (array == null || array.length == 0) {
            throw new NullPointerException();
        }
        int len = array.length;
        for (int i = 0; i < len; i++) {
            int tmp;
            for (int j = len - 1; j > i; j--) {
                if (array[j] < array[j - 1]) {
/*                    tmp = array[j];
                    array[j] = array[j - 1];
                    array[j - 1] = tmp;*/
                    swap(array, j, j - 1);
                }
                printAll(array);
            }
        }
    }

    public static void bubbleSortOptmize(int[] array) {
        if (array == null || array.length == 0) {
            throw new NullPointerException();
        }
        int len = array.length;
        for (int i = 0; i < len; i++) {
            int tmp;
            boolean flag=false;
            for (int j = len - 1; j > i; j--) {
                if (array[j] < array[j - 1]) {
/*                    tmp = array[j];
                    array[j] = array[j - 1];
                    array[j - 1] = tmp;*/
                    swap(array, j, j - 1);
                    flag = true;
                }
                printAll(array);
                if (flag == false) {
                    return;
                }

            }
        }
    }

    /*    形式参数的交换无法使得真实参数交换
    public static void swap(int src, int des) {
            int tmp = 0;
            tmp = src;
            src = des;
            des = tmp;
        }*/
    public static void swap(int[] array, int src, int des) {
        int tmp;
        tmp = array[src];
        array[src] = array[des];
        array[des] = tmp;
    }

    public static void printAll(int[] array) {
        log.info(Arrays.toString(array));
    }
}

结果

2019-08-19 20:13:15,069   [main] INFO  BubbleSortTest  - [1, 2, 3, 4, 5, 6]