面试中常用的算法总结

面试中难免会问到一些排序算法，最常见的无非是冒泡排序，选择排序，快速排序，今天先来学习这三个算法，大家应该都会，我只是作为总结，记录下

随机数组如下

int[] sortArray = new int[]{2, 1, 2, 7, 4, 6, 8, 10};

一 冒泡排序

   一列数组从小到大进行冒泡排序，两层for循环，时间复杂度为O(n²)

//冒泡排序
private void BubbleSort(int[] sortArray) {
    if ((sortArray == null) || (sortArray.length == 0))
        return;
 int temp;
 for (int i = 0; i length - 1; i++) {
        for (int j = i + 1; j length; j++) {
            if (sortArray[i] > sortArray[j]) {
                temp = sortArray[i];
 sortArray[i] = sortArray[j];
 sortArray[j] = temp;
 }
        }
    }
    for (int i = 0; i length; i++) {
        Log.e(getClass().getSimpleName() + "bubbleSort ", String.valueOf(sortArray[i]));
 }
}

冒泡log输出如下

11:57:45.870 12101-12101/com.asiatravel.asiatravel E/MainActivitybubbleSort: 1
11:57:45.870 12101-12101/com.asiatravel.asiatravel E/MainActivitybubbleSort: 2
11:57:45.870 12101-12101/com.asiatravel.asiatravel E/MainActivitybubbleSort: 2
11:57:45.870 12101-12101/com.asiatravel.asiatravel E/MainActivitybubbleSort: 4
11:57:45.870 12101-12101/com.asiatravel.asiatravel E/MainActivitybubbleSort: 6
11:57:45.870 12101-12101/com.asiatravel.asiatravel E/MainActivitybubbleSort: 7
11:57:45.870 12101-12101/com.asiatravel.asiatravel E/MainActivitybubbleSort: 8
11:57:45.870 12101-12101/com.asiatravel.asiatravel E/MainActivitybubbleSort: 10

二 选择排序

    选择排序是冒泡的升级版，时间复杂度为O(n²)

//选择排序
private void selectSort(int[] a) {
    int minIndex = 0;
    int temp = 0;
    if ((a == null) || (a.length == 0))
        return;
    for (int i = 0; i length - 1; i++) {
        minIndex = i;//无序区的最小数据数组下标
        for (int j = i + 1; j length; j++) {
            //在无序区中找到最小数据并保存其数组下标
            if (a[j]                 minIndex = j;
            }
        }
        if (minIndex != i) {
            //如果不是无序区的最小值位置不是默认的第一个数据，则交换之。
            temp = a[i];
            a[i] = a[minIndex];
            a[minIndex] = temp;
        }
    }
    for (int i = 0; i length; i++) {
        Log.e(getClass().getSimpleName() + "selectSort ", String.valueOf(a[i]));
    }
}

11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityselectSort: 1
11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityselectSort: 2
11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityselectSort: 2
11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityselectSort: 4
11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityselectSort: 6
11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityselectSort: 7
11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityselectSort: 8
11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityselectSort: 10

三 快速排序

   快速排序也是冒泡的升级版，时间复杂度为O(n²)

//快速排序
private void quickSort(int[] arr, int low, int high) {
    int l = low;
    int h = high;
    int povit = arr[low];
    while (l         while (l = povit)
            h--;
        if (l             int temp = arr[h];
            arr[h] = arr[l];
            arr[l] = temp;
            l++;
        }
        while (l             l++;
            if (l                 int temp = arr[h];
                arr[h] = arr[l];
                arr[l] = temp;
                h--;
            }
        }
        System.out.print("quickSort " + "l=" + (l + 1) + "h=" + (h + 1) + "povit=" + povit + "\n");
        if (l > low) quickSort(arr, low, l - 1);
        if (h , l + 1, high);
    }
    for (int i = 0; i length; i++) {
        Log.e(getClass().getSimpleName() + "quickSort ", String.valueOf(arr[i]));
    }
}

输出 log如下

11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityquickSort: 1
11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityquickSort: 2
11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityquickSort: 2
11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityquickSort: 4
11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityquickSort: 6
11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityquickSort: 7
11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityquickSort: 8
11:59:24.910 12858-12858/com.asiatravel.asiatravel E/MainActivityquickSort: 10

关于时间复杂度，请移步这篇博客，针对性的对比算法复杂度，总结的挺好

http://blog.csdn.net/wuxinyicomeon/article/details/5996675/

还有不明白的，百度百科介绍的很详细，我也是做个笔记记录下，与君共勉！