二分法模板

package main

import "fmt"

//二分法最关键的地方在于：确定target元素位于哪个区间？ (left, mid) or (mid, right)

func solution(nums []int, target int) int {
	if nums == nil {
		return -1
	}

	left, right := 0, len(nums)-1

	for left <= right { /*注意循环条件为： left <= right*/
		mid := left + (right-left)>>1 //left+right可能会出现溢出导致除以2时获取的值有误

		if nums[mid] == target { /*找到了元素*/
			return mid
		} else if nums[mid] < target { //向右移动， 注意: left = mid + 1
			left = mid + 1
		} else if nums[mid] > target { //向左移动， 注意: right = mid - 1
			right = mid - 1
		}
	}

	return -1
}

func main() {
	fmt.Println(solution([]int{1, 2, 3, 4, 5, 6, 7, 8, 9}, 3))
	fmt.Println(solution([]int{1, 2, 3, 4, 5, 6, 7, 8, 9}, 5))
	fmt.Println(solution([]int{1, 2, 3, 4, 5, 6, 7, 8, 9}, 30))
	fmt.Println(solution([]int{1, 2, 3, 4, 5, 6, 7, 8, 9}, 0))
	fmt.Println(solution([]int{1, 2, 2, 2, 2}, 2))
	fmt.Println(solution([]int{1}, 1))
}