返回指定值的下标

题目

给定一个含有n个元素升序的整型数组nums和一个目标值target，写一个函数搜索nums中的target，如果目标值存在则返回目标值的下标，否则返回-1. 示例1：

输入：nums=[-1, 0, 3, 5, 7, 11], target=5
输出：3
解释：5出现在nums中并且下标为3

解法1：二分法

class Solution {
    public int search(int[] nums, int target) {
        int left=0;
        int right=nums.length-1;
        while(left<=right){ //在[left...right]里查找target
            int mid=left+(right-left)/2; //为了防止left+right整型溢出，写成这样
            if(nums[mid]==target){
                return mid;
            }else if(nums[mid]<target){ //下一轮搜索区间 [mid+1...right]
                left=mid+1;
            }else{ //此时nums[mid]>target，下一轮搜索区间 [left...mid-1]
                right=mid-1;
            }
        }    
        return -1;
    }
}

class Solution {
  search(nums, target) {
    let left = 0;
    let right = nums.length - 1;
    while (left <= right) {
      let mid = Math.floor(left + (right - left) / 2);
      if (nums[mid] === target) {
        return mid;
      } else if (nums[mid] < target) {
        left = mid + 1;
      } else {
        right = mid - 1;
      }
    }
    return -1;
  }
}

const solution = new Solution();
const nums = [1, 2, 3, 4, 5];
const target = 3;
const result = solution.search(nums, target);
console.log(result);

class Solution:
    def search(self, nums, target):
        left = 0
        right = len(nums) - 1
        while left <= right:
            mid = left + (right - left) // 2
            if nums[mid] == target:
                return mid
            elif nums[mid] < target:
                left = mid + 1
            else:
                right = mid - 1
        return -1

package main

import "fmt"

func search(nums []int, target int) int {
	left := 0
	right := len(nums) - 1
	for left <= right {
		mid := left + (right-left)/2
		if nums[mid] == target {
			return mid
		} else if nums[mid] < target {
			left = mid + 1
		} else {
			right = mid - 1
		}
	}
	return -1
}

func main() {
	nums := []int{1, 2, 3, 4, 5}
	target := 3
	result := search(nums, target)
	fmt.Println(result)
}