C++ 二分查找 binary search 模板

#include<iostream>
#include<cstdlib>
#include<cstdio>
#include<memory.h>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<vector>
#include<queue>

#define mem(array)  memset((array),0,sizeof((array)))
#define Qsort(array,len,cmp) qsort(array,len,sizeof(array[0]),cmp)

#define inf 0x7fffffff
#define MAXN 10+100

using namespace std;


int binarySearch(int* a, int n, int x, int flag = -1)
{   /**
    binarySearch parameter description:
    int * a     a is an array that sorted from small to large
    int n       n is the length of array a
    int x       x is the search object
    int flag    flag is a return sign.
    the function will return the index of the first object that equal to the value of object x if the object exists.
        when the object is not exist, the function will return -1 while flag is -1,
        or return the index of the last maximal object that less than the value of object x.
    從長度爲n、已經從小到大排序好的數組a中查找值x的位置，
    若存在，返回第一個等於x值的下標，否則返回-1（flag=-1時）或者比x小的最後面一個最大的值（flag！=-1）
    */

    if(x < a[0])
        return -1;
    if(x > a[n-1])
        if(flag == -1)
            return -1;
        else
            return n-1;
    int l = 0;
    int r = n-1;
    int mid;
    bool getAns = false;
    while(l <= r){
        mid = (l+r)>>1;
        if(x == a[mid]) {getAns = true; break;}
        if(x < a[mid])  {r = mid-1; continue;}
        if(x > a[mid])  {l = mid+1; continue;}
    }
    if(getAns){
        while(mid >= 0 && x == a[mid])
            --mid;
        return mid+1;
    }
    else{
        if(flag == -1)
            return -1;
        else
            return r;
    }
}

/** refer to the following call*/
int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",tdout);

    int ans;
    int x;

    int a[MAXN];
    for(int i = 0; i < MAXN; ++i)
        a[i] = i<<1;
    for(int i = 0; i < MAXN; ++i)
        printf("%d ",a[i]);
    cout<<endl;
    while(cin>>x){
        ans = binarySearch(a,MAXN,x,1);
        cout << ans <<endl;
    }
    return 0;
}