public class BinarySearch {
	static int[] arr = {1, 3, 5, 7, 8, 10, 20, 35, 99, 100};

	public static void main(String[] args) {
		System.out.println("1. 순환 호출을 이용한 이진 탐색");
		System.out.println(binarySearch1(5, 0, arr.length-1)); // 2
		
		System.out.println("\\n2. 반복을 이용한 이진 탐색");
		System.out.println(binarySearch2(20, 0, arr.length-1)); // 6
		
	}
	
	// 재귀적 탐색
	static int binarySearch1(int key, int low, int high) {
		int mid;
		
		if(low <= high) {
			mid = (low + high) / 2;
			
			if(key == arr[mid]) { // 탐색 성공 
				return mid;
			} else if(key < arr[mid]) {
				return binarySearch1(key ,low, mid-1); // 왼쪽 부분 탐색 
			} else {
				return binarySearch1(key, mid+1, high); // 오른쪽 부분 탐색 
			}
		}
		
		return -1; // 탐색 실패 
	}
	
	// 반복적 탐색
	static int binarySearch2(int key, int low, int high) {
		int mid;
		
		while(low <= high) {
			mid = (low + high) / 2;
			
			if(key == arr[mid]) {
				return mid;
			} else if(key < arr[mid]) {
				high = mid - 1;
			} else {
				low = mid + 1;
			}
		}
		
		return -1; // 탐색 실패 
	}

}

Quiz : 32가 몇번째에 위치하는가

public class MyClass {
    
   static int[] arr = {23, 87, 65, 12, 57, 32, 99, 81};
    
    public static void main(String args[]) {
     System.out.println(binarySearch2(32, 0, arr.length-1)); // 2
    }
    
    // 반복적 탐색
	static int binarySearch2(int key, int low, int high) {
		int mid;
		
		while(low <= high) {
			mid = (low + high) / 2;
			
			if(key == arr[mid]) {
				return mid;
			} else if(key < arr[mid]) {
				high = mid - 1;
			} else {
				low = mid + 1;
			}
		}
		
		return -1; // 탐색 실패 
	}
}