输入连续有序数组，数组中有一个数字丢失，二分查找

#include <iostream>

using namespace std;

int func(int *index,int begin,int end){
if(begin>end){
return NULL;
}
int i = begin;
int j = end;
while(i<j){
int p = i + ((j-i)>>1);
if(index[p]-index[0] == p){
i = p+1;
}else if(index[p]-index[0]>p){
j = p;
}
}
return j+index[0];
}
int main(){
int index[] = {1,2,3,5,6};
int ret = func(index,0,5);
cout << ret << endl;
}