/*
	Jia Tse
	CS477 - Algorithm Analysis
	Algorithm from COMPUTER ALGORITHMS C++ - Ellis Horowitz
	02/25/06
	
	binary search
*/

#include <iostream>

using namespace std;

#define m 5

int a[m] = {1,2,3,4,8};
int b[m];

int binarySearch(int a[], int n, int x){
	/* Given an array a[0:n] of elements in nondecreasing
	 * order, n>=0, determine whether x is present, and
	 * if so, return j such tht x == a[j]; else return -1.
	 */
	 
	 int low = 0, high = n;
	 int mid;
	 
	 while (low<=high){
	 	mid = (low+high)/2;
	 	if (x<a[mid])	high = mid-1;
	 	else if (x >a[mid])	low = mid+1;
	 	else return (mid);
	 }
	 return (-1);	
}

int main(){
	int index;
	
	index = binarySearch(a, m-1, 1);
	if (index == -1)
		cout<<"1 does not exist"<<endl;
	else
		cout<<"1 is at index "<<index<<endl;
		
	index = binarySearch(a, m-1, 5);
	if (index == -1)
		cout<<"5 does not exist"<<endl;
	else
		cout<<"5 is at index "<<index<<endl;	

	return 0;
}