二分查找

#include <iostream>
using namespace std;


int doubleBinary(int* num, int a, int b,int target) {

	if (a > b) {
		return -1;
	}
	int mid = (a + b)/2;
	if (num[mid] == target)
		return mid;

	if (target > num[mid])
		return doubleBinary(num, mid + 1, b, target);
	else {
		return doubleBinary(num, a , mid-1, target);

	}
	return -1;
}

int forResult(int* num,int a,int b,int target) {

	int l = a;
	int r = b;

	while (l <= r) {

		int mid = (l+r)/ 2;
		if (num[mid] == target)
			return mid;
		if (num[mid] < target) {
			l = mid + 1;
		}
		else {
			r = mid - 1;
		}

	}
	return -1;

}



int main() {

	int a[5] = { 1,3,5,7,9 };
	int ret;
	//ret = doubleBinary(a,0,4,2);
	ret = forResult(a, 0, 4, 2);

	cout << ret << endl;
	return 0;
}