Solution.cs

public class Solution {
    public int ThreeSumClosest(int[] nums, int target) {
        Array.Sort(nums);
        int ans = 1 << 30;
        int n = nums.Length;
        for (int i = 0; i < n; ++i) {
            int j = i + 1, k = n - 1;
            while (j < k) {
                int t = nums[i] + nums[j] + nums[k];
                if (t == target) {
                    return t;
                }
                if (Math.Abs(t - target) < Math.Abs(ans - target)) {
                    ans = t;
                }
                if (t > target) {
                    --k;
                } else {
                    ++j;
                }
            }
        }
        return ans;
    }
}