[Leetcode] 16 - 3Sum Closest

原题链接：https://oj.leetcode.com/problems/3sum-closest/

这道题基本就是3sum的变形，就直接按照3sum先排序，然后取当前数，再左右指针对于后面的数组向内扫描，但是因为是求closest，只有diff = 0的时候才能完全跳出当前循环，否则则需要继续扫描直到相遇或diff = 0。

所以复杂度是排序时间加上扫描时间O(nlogn + n^2)

class Solution {
public:
int threeSumClosest(vector<int> &num, int target) {
int diff = INT_MAX;
int res = 0;
sort(num.begin(), num.end());

for (int i = 0; i < num.size() - 2; ++i) {
int left = i + 1;
int right = num.size() - 1;

while (left < right) {
int curSum = num[i] + num[left] + num[right];
if (curSum == target) {
return curSum;
} else if (curSum > target) {
if (abs(curSum - target) < diff) {
diff = abs(curSum - target);
res = curSum;
}
--right;
} else {
if (abs(curSum - target) < diff) {
diff = abs(curSum - target);
res = curSum;
}
++left;
}
}
}

return res;
}
};