# 704. Binary Search 二分查找

@TOC

## # 题目描述

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]`.

## # 解题方法

### # 线性查找

``````class Solution(object):
def search(self, nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: int
"""
try:
return nums.index(target)
except:
return -1
``````

### # 二分查找

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

``````class Solution(object):
def search(self, nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: int
"""
N = len(nums)
left, right = 0, N
# [0, N)
while left < right:
mid = left + (right - left) / 2
if nums[mid] == target:
return mid
elif nums[mid] > target:
right = mid
else:
left = mid + 1
return -1
``````

## # 日期

2018 年 7 月 12 日 —— 天阴阴地潮潮，已经连着两天这样了 2018 年 11 月 21 日 —— 又是一个美好的开始