C++学习之路： 循环实现二分查找

#include <iostream>
#include <string>
#include <vector>
using namespace std;

int BinSearch(vector<int> ivec, int key)   //循环实现的二分查找要比递归实现效率要高很多，推荐使用这种方法
{
    int low = 0, high = ivec.size() -1, mid;  //注意high的边界值，ivec.size()指向的是最后一个元素的下一个元素（即指向越界的内存）;
    if(ivec[low] == key)
        return low;
    if(ivec[high] == key)
        return high;
    mid = low + (high - low) / 2;

    if(ivec[mid] == key)
        return mid;
    if(ivec[mid] > key)
        high = mid - 1;
    if(ivec[mid] < key)
        low = mid + 1;

    if(low > high)
        return -1 //没有找到则返回 -1；
}


int main(int argc, const char *argv[])
{
    
    return 0;
}

以下是实现的代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <iostream>
#include <string>
#include <vector>
#include <fcntl.h>
#include <unistd.h>
#include <sys/time.h>
#include <algorithm>
#define ERR_EXIT(m) 
    do { 
        perror(m);
        exit(EXIT_FAILURE);
    }while(0)
using namespace std;

const int size = 1000000;

int binarySearch(vector<int> vec, int key)
{
    int low = 0, high = vec.size() - 1, mid;
    while(low <= high)
    {
        if(vec[low] == key)
            return low;
        if(vec[high] == key)
            return high;
        mid = low + ((high - low) / 2);
        if(vec[mid] == key)
            return mid;
        else if(vec[mid] > key)
            high = mid - 1;
        else
            low = mid + 1;
    }
    if(low > high)
        return -1;
}

int binarySearch2(vector<int> vec, int low, int high, int key)
{
    int mid = low + (high - low) / 2;
    if(low > high)
        return -1;
    else
    {
        if(vec[mid] == key)
            return mid;
        else if(vec[mid] > key)
            return binarySearch2(vec, low, mid - 1, key);
        else 
            return binarySearch2(vec, mid + 1, high, key);
    }
}
int main(int argc, const char *argv[])
{
    time_t starttime = time(NULL);
    FILE *fp1 = fopen("largeW.txt", "rb");
    FILE *fp2 = fopen("largeT.txt", "rb");
    if(fp1 == NULL || fp2 == NULL)
    {
        ERR_EXIT("fopen"); 
    }

    vector<int> ivec;
    int val, cnt = 0;
    while(fscanf(fp1, "%d", &val) == 1)
    {
        ivec.push_back(val);
    }
    sort(ivec.begin(), ivec.end());
  
    while(fscanf(fp2, "%d", &val) == 1)
    {
        //if(binarySearch2(ivec, 0, ivec.size() - 1, val) >= 0)
        if(binarySearch(ivec, val) >= 0)
            continue;
        else
        {
            cout << val << " ";
            cnt++;
        }
    }
    cout << endl << cnt << endl;
    
    fclose(fp1);
    fclose(fp2);
    time_t endtime = time(NULL);
    time_t cost = endtime - starttime;
    cout << "time cost : " << cost << "s" << endl;
    return 0;
}