编程算法 - 快速排序(QuickSort)和二分查找(BinarySearch)

快速排序(QuickSort)和二分查找(BinarySearch)

本文地址: http://blog.csdn.net/caroline_wendy

快速排序和二分查找的定义, 网上书上都有, 本文主要是讲解如何写出这两个经典算法.

程序员必须掌握的两种算法, 使用任何语言, 使用纸都是必须的.

快速排序(C):

 /*
  * main.cpp
  *
  *  Created on: 2014年9月10日
  *      Author: Spike
  */

 #include <stdio.h>
 #include <stdlib.h>
 #include <iostream>
 #include <exception>

 int RandomInRange(int start, int end) {
     int res = rand()%(end-start+1) + start;
     return res;
 }

 void Swap(int* num1, int* num2) {
     int tmp = *num1;
     *num1 = *num2;
     *num2 = tmp;
 }

 int Partition(int data[], int length, int start, int end) {
     if (data == NULL || length <= 0 || start > end || start < 0 || end >= length) {
         return -1;
     }

     int index = RandomInRange(start, end);
     Swap(&data[index], &data[end]);
     int small = start-1;
     for (index = start; index < end; ++index) {
         if (data[index] < data[end]) {
             small++;
             if (small != index)
                 Swap(&data[index], &data[small]);
         }
     }
     small++;
     Swap(&data[small], &data[end]);
     return small;
 }

 void QuickSort(int data[], int length, int start, int end) {
     if (start == end)
         return;
     int index = Partition(data, length, start, end);
     if (index > start)
         QuickSort(data, length, start, index-1);
     if (index < end)
         QuickSort(data, length, index+1, end);
 }

 int main(void) {
     int data[] = {1, 4, 5, 2, 3, 7, 8, 6};
     int length = 8;
     QuickSort(data, length, 0, length-1);
     for (int i=0; i<length; ++i) {
         printf("%d ", data[i]);
     }
     printf("\n");
     return 0;
 }

二分查找(C):

 /*
  * main.cpp
  *
  *  Created on: 2014年9月10日
  *      Author: Spike
  */

 #include <stdio.h>
 #include <stdlib.h>
 #include <iostream>
 #include <exception>

 int BinarySearch(int data[], int length, int value) {
     int left = 0;
     int right = length-1;
     while (left <= right) {
         int middle = left + ((right-left)>>1);
         if (data[middle] > value)
             right = middle - 1;
         else if (data[middle] < value)
             left = middle + 1;
         else
             return middle;
     }
     return -1;
 }

 int main(void) {
     int data[] = {1, 2, 3, 4, 5, 6, 7, 8};
     int length = 8;

     printf("%d ", BinarySearch(data, length, 5));

     printf("\n");
     return 0;
 }