LeetCode#16 3 Sum Closest

Problem Definition:

Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

 For example, given array S = {-1 2 1 -4}, and target = 1.

    The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

Solution:

结构基本上跟#15一样样的。只是这里要求最接近的一个和，即求 sum，使得 | target-sum | 最小。

绝对值的取值，最小也就是0了，所以一旦找到这样一个sum==target，就可以直接退出了。在OJ上一跑，发现测试的例子里还真不少这种，存在某三个数，其和刚好是target这么大。

 1 # @param {integer[]} nums
 2     # @param {integer} target
 3     # @return {integer}
 4     def threeSumClosest(nums, target):
 5         nums.sort()
 6         first=0
 7         finalFirst=len(nums)-3
 8         rightBound=len(nums)-1
 9         minGap=sys.maxint
10         klz=0
11         while first<=finalFirst:
12             lft=first+1
13             rgt=rightBound
14             nf=nums[first]
15             while lft<rgt:
16                 nl=nums[lft]
17                 nr=nums[rgt]
18                 thr=nf+nl+nr
19                 gap=abs(thr-target)
20                 if gap<minGap:
21                     minGap=gap
22                     klz=thr
23                 if thr>target:
24                     rgt-=1
25                 elif thr<target:
26                     lft+=1
27                 else:    #crux
28                     return klz
29 
30             while first<=finalFirst and nums[first]==nf:
31                 first+=1
32         return klz