[leetcode 16] 3Sum Closest

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).

思路：同3Sum， 排序之后，夹逼

class Solution {
public:
int threeSumClosest(vector<int> &num, int target) {
int res;
if (num.size() < 3) {
return res;
}
int min_gap = INT_MAX;  //记录最小的差值
sort(num.begin(), num.end());
auto last = num.end();
for (auto i = num.begin(); i < last - 2; i++) {
auto j = i + 1;
auto k = last - 1;
while (j < k) {
int sum = *i + *j + *k;
int gap = abs(sum - target);
if (gap < min_gap) {
res = sum;
min_gap = gap;
}
if (sum > target) {
k--;
} else {
j++;
}
}
}
return res;
}
};