LeetCode 704. Binary Search

Posted 2020-11-22 Dylan_Java_NYC

原题链接在这里：https://leetcode.com/problems/binary-search/

题目：

Given a sorted (in ascending order) integer array nums of n elements and a target value, write a function to search target in nums. If target exists, then return its index, otherwise return -1.

Example 1:

Input: nums = [-1,0,3,5,9,12], target = 9
Output: 4
Explanation: 9 exists in nums and its index is 4

Example 2:

Input: nums = [-1,0,3,5,9,12], target = 2
Output: -1
Explanation: 2 does not exist in nums so return -1

Note:

1. You may assume that all elements in nums are unique.
2. n will be in the range [1, 10000].
3. The value of each element in nums will be in the range [-9999, 9999].

题解：

Use binary search to guess.

Time Complexity: O(logn).n = nums.length.

Space: O(1).

AC Java:

 1 class Solution {
 2     public int search(int[] nums, int target) {
 3         if(nums == null || nums.length == 0){
 4             return -1;
 5         }
 6         
 7         int l = 0;
 8         int r = nums.length-1;
 9         while(l <= r){
10             int mid = l + (r-l)/2;
11             if(nums[mid] < target){
12                 l = mid + 1;
13             }else if(nums[mid] > target){
14                 r = mid-1;
15             }else{
16                 return mid;
17             }
18         }
19         
20         return -1;
21     }
22 }

跟上Search in a Sorted Array of Unknown Size.