public:

int threeSumClosest(vector<int>& nums, int target) {

// Same as 3 sum, but instead of keeping track of a list of solutions,

// keep track of closest sum.

int res = 0;

int min_d = INT_MAX;

int n = nums.size();

sort(nums.begin(), nums.end());

for (int i = 0; i < n - 2; ++i) {

if (i != 0 && nums[i] == nums[i - 1]) continue;

int left = i + 1;

int right = n - 1;

while (left < right) {

int curr_sum = nums[i] + nums[left] + nums[right];

int curr_d = abs(curr_sum - target);

if (curr_d < min_d) {

res = curr_sum;

min_d = curr_d;

}

// Move the sum closer

if (curr_sum > target) {

// Overshot, so decrease curr_sum

--right;

} else if (curr_sum < target) {

// Undershot, increase curr_sum

++left;

} else {

// jackpot (exact match)

return curr_sum;

}

}

}

return res;

}