二分查找的实现

C++

#include<bits/stdc++.h>
using namespace std;

int binary_search( int arr[], int num, int item ){
	int low = 0;
	int high = num-1;
	while( low <= high ){
		int mid = (low + high)/2;
		int midValue = arr[mid];
		if( midValue==item ){
			return mid;
		}
		if( midValue<item ) {
			low = mid+1;
		} else {
			high = mid-1;
		}
		// cout<<mid<<" "<<low<<" "<<high<<endl;
	}
	return -1;
}

int main(){
	int arr[] = { 1, 3, 5, 7, 9 };
	int item = 2;
	int index = binary_search( arr, sizeof(arr) / sizeof(arr[0]), item );
	if( index == -1 ){
		cout<<"None"<<endl;
	} else {
		cout<<index<<endl;
	}
	return 0;
}

JS

function binary_search( arr, item ){
	let low = 0;
	let high = arr.length - 1;
	while( low<=high ){
		let mid = Math.floor(( low + high )/2)
		if( arr[mid] == item ){
			return mid;
		}
		if( arr[mid]<item ){
			low = mid+1;
		} else {
			high = mid-1;
		}
		// console.log( mid,low,high )
	}
	return "None";
}

let arr = [1,3,5,7,9];
console.log( binary_search(arr,3) )
console.log( binary_search(arr,5) )
console.log( binary_search(arr,2) )
console.log( binary_search(arr,-1) )