c_cpp 在有序数组中查找元素的位置

Posted 2021-05-14

// https://www.geeksforgeeks.org/find-position-element-sorted-array-infinite-numbers/
#include <iostream>
using namespace std;

int binary (int a[],int l, int r, int x){
    if (l<=r){
        int m=(l+r)/2;
        if (a[m]==x)
            return m;
        if (a[m]>x)
            return binary(a,l,m-1,x);
        return binary(a,m+1,r,x);
    }
    return -1;
}

int main(){
    int n,x;
    cin>>n;
    int a[n];
    for (int i=0;i<n;i++)
        cin>>a[i];
    cout << "Enter the search element: ";
    cin >>x;

    int l=0,r=1,k=a[0];
    while (k<x){
        l = r;
        r = 2*r;
        k = a[r];
    }
    int j=binary(a,l,r,x);
    cout<< "Index at "<<j;
}