二分查找(循环/递归)实现

1.Java实现

• 循环式

public static int binarySearch(int[] array, int key) {
	int low = 0, high = array.length - 1;
	while (low <= high) {
		int mid = (low + high) / 2;
		if (array[mid] > key) {
			high = mid - 1;
		} else if (array[mid] < key) {
			low = mid + 1;
		} else {
			return mid;
		}
	}
	return -1;
}

• 递归式

public static int binarySearch(int[] array, int key, int low, int high) {
	int mid = (low + high) / 2;
	if (array[mid] > key) {
		high = mid - 1;
		if (low > high) {
				return -1;
		}
		return binarySearch(array, key, low, high);
	} else if (array[mid] < key) {
		low = mid + 1;
		if (low > high) {
				return -1;
		}
		return binarySearch(array, key, low, high);
	} else {
		return mid;
	}
}

2.Golang实现

package main

import (
	"fmt"
)

func main() {
	a := []int{1, 3, 4, 5, 6}
	key := 7
	i := BinarySearch(a, 0, len(a)-1, key)
	fmt.Println(key, "is:", "array[", i, "]")
}

/*
return -1 : not find & illeage bounds
return index : find key
*/
func BinarySearch(a []int, left int, rigth int, key int) int {
	if left > rigth {
		return -1
	}
	mid := (left + rigth) / 2
	if a[mid] > key {
		return BinarySearch(a, left, mid-1, key)
	}
	if a[mid] < key {
		return BinarySearch(a, mid+1, rigth, key)
	}
	return mid
}