[LeetCode 16] 3Sum Closest

 1 class Solution {
 2 public:
 3     int threeSumClosest(vector<int> &num, int target) {
 4         int result = 0;
 5         int min_gap = INT_MAX;
 6 
 7         sort(num.begin(), num.end()); // 排序
 8 
 9         auto last = num.end();
10         for (auto a = num.begin(); a < prev(last, 2); ++a) {
11             auto b = next(a);
12             auto c = prev(last);
13             while (b < c) {
14                 const int sum = *a + *b + *c;
15                 const int gap = abs(sum - target);
16 
17                 if (gap < min_gap) {
18                     result = sum;
19                     min_gap = gap;
20                 }
21 
22                 if (sum < target)
23                     ++b;
24                 else
25                     --c;
26             }
27         }
28 
29         return result;
30     }
31 };