leetcode16 3Sum Closest

Posted 2021-03-08 yawenw

 1 """
 2 Given an array nums of n integers and an integer target, find three integers in nums such that the sum is closest to target. Return the sum of the three integers. You may assume that each input would have exactly one solution.
 3 Example:
 4 Given array nums = [-1, 2, 1, -4], and target = 1.
 5 The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).
 6 """
 7 """
 8 双指针法
 9 """
10 class Solution1:
11     def threeSumClosest(self, nums, target):
12         nums.sort()
13         res = nums[0] + nums[1] + nums[2]
14         for i in range(len(nums)-2):
15             # bug 有了下面这个 对于[0,0,0] 过不去
16             # if nums[i] == [i+1]:
17             #     continue
18             j = i + 1
19             k = len(nums)-1
20             while j < k:
21                 n = nums[i] + nums[j] + nums[k]
22                 if n == target:
23                     return n
24                 if abs(n - target) < abs(res - target):
25                     res = n
26                 if n > target:  #！！！终止条件,写的时候没有考虑到
27                     k -= 1
28                 elif n < target:
29                     j += 1
30         return res
31 
32 
33 """
34 自己的想法暴力解法，三层循环
35 超时
36 """
37 class Solution2:
38     def threeSumClosest(self, nums, target):
39         temp = float(‘inf‘)
40         for i in range(len(nums)):
41             j = i + 1
42             for j in range(j, len(nums)):
43                 k = j + 1
44                 for k in range(k, len(nums)):
45                     n = nums[i] + nums[j] +nums[k]
46                     if abs(n-target) < temp:
47                         temp = abs(n-target)
48                         res = n
49         return res