LeetCode 704. Binary Search
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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 innums
and its index is 4
Example 2:
Input:nums
= [-1,0,3,5,9,12],target
= 2 Output: -1 Explanation: 2 does not exist innums
so return -1
Note:
- You may assume that all elements in
nums
are unique. n
will be in the range[1, 10000]
.- 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 }
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