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。

# @param {integer[]} nums
    # @param {integer} target
    # @return {integer}
    def threeSumClosest(nums, target):
        nums.sort()
        first=0
        finalFirst=len(nums)-3
        rightBound=len(nums)-1
        minGap=sys.maxint
        klz=0
        while first<=finalFirst:
            lft=first+1
            rgt=rightBound
            nf=nums[first]
            while lft<rgt:
                nl=nums[lft]
                nr=nums[rgt]
                thr=nf+nl+nr
                gap=abs(thr-target)
                if gap<minGap:
                    minGap=gap
                    klz=thr
                if thr>target:
                    rgt-=1
                elif thr<target:
                    lft+=1
                else:    #crux
                    return klz

            while first<=finalFirst and nums[first]==nf:
                first+=1
        return klz