https://oj.leetcode.com/problems/3sum-closest/
class Solution:
# @return an integer
def threeSumClosest(self, num, target):
num.sort()
n = len(num)
if (n < 3): return
ans = sum(num[0:3])
for i in range(n - 2):
j, k = i + 1, n - 1
while j < k:
if abs(num[i] + num[j] + num[k] - target) < \
abs(ans - target):
ans = num[i] + num[j] + num[k]
if num[i] + num[j] + num[k] < target:
j += 1
else:
k -= 1
return ans