剑指offer-面试题53_3-数组中数值和下标相等的元素-二分查找

Posted 2021-03-21 buaazhhx

/*
题目：
	求单调递增数组中，数值与下标相等的任意数字。
*/
/*
思路：
	二分法。
*/
#include<iostream>
#include<cstring>
#include<vector>
#include<algorithm>
#include<map>


using namespace std;

int getNumberSameAsIndex(vector<int> &A, int n){
    if(n <= 0 || A.empty()) return -1;
    int start = 0;
    int end = n - 1;

    while(start <= end){
        int middle = (start + end) / 2;
        if(A[middle] < middle){
            start = middle + 1;
        }else if(A[middle] > middle){
            end = middle - 1;
        }else{
            return middle;
        }
    }

    return -1;
}

int main(){
   vector<int> a = {-3,-1,1,3,5};
   cout<<getNumberSameAsIndex(a,5);
}