二分查找

int bsearch(int a[],int l,int r,int x)
{     
    int m;
    while(l<=r){    
        m = (l+r)/2;  // m = l+(r-l)>>2;
        if(a[m]==x)
            return m;
        else if(a[m]>x) 
            r = m-1;
        else
            l = m+1;
    }
    return -1; //查找不成功
}

int bsearchLower(int a[],int l,int r,int x)
{
    int m;
    while(l<r){
        m = (l+r)/2;
        if(x<=a[m])  
            r = m;
        else  
            l = m+1;
    }
    if(a[l]==x) 
        return l;
    else 
        return -1;    //查找不成功
}

int bsearchUpper(int a[],int l,int r,int x)
{
    int m;
    while(l<r){
        m = (l+r+1)/2;     //加了“1”
        if(x<a[m])  
            r = m-1;
        else   
            l = m;
    }
    if(a[r]==x) 
        return r;
    else 
        return -1;//查找不成功
}