二分 第一次出现的位置，最后一次出现的位置

#include<stdio.h>
#include<iostream>
#include<string.h>
using namespace std;

class mysolve
{
public:

    int a[20];
    int binary_first(int a[],int len,int key)//第一次出现的位置
    {
        int left=0;
        int right=len-1;
        while(left<right)
        {
            int mid=(left+right)/2;
            if(a[mid]<key)
                left=mid+1;
            else
                right=mid;


        }
        if(a[left]==key)
            return left;
        return -1;
    }

    int binary_second(int a[],int len,int key)//最后一次出现的位置
    {
        int left=0;
        int right=len-1;
        while(left<right-1)
        {
            int mid=(left+right)/2;
            if(a[mid]>key)
               right=mid-1;
            else  left=mid;

        }
        if(a[right]==key)
            return right;
        else if(a[left]==key)
            return left;
        else return -1;
    }
    int putong(int a[],int len,int key)
    {
        int left=0;
        int right=len-1;
        while(left<=right)
        {
            int mid=(left+right)/2;
            if(a[mid]<key)
                left=mid+1;
            else if(a[mid]==key)
                return mid;

            else
                right=mid-1;
        }
        return -1;
    }


};



int main()
{
    mysolve solve;

    int z[20]= {1,2,2,2,2,2,2,2,2,2,3};
    memcpy(solve.a,z,sizeof(int)*20);
    cout<<solve.binary_first(solve.a,11,2)<<endl;
    cout<<solve.binary_second(solve.a,11,2)<<endl;
    cout<<solve.putong(solve.a,11,2);

}