feat(src): add 16-threeSumClosest

Author: kwu130

src/16-threeSumClosest.cpp

@@ -0,0 +1,50 @@
+//
+// Created by 1412 on 2025/10/12.
+//
+
+#include <bits/stdc++.h>
+
+using namespace std;
+
+class Solution {
+public:
+    int threeSumClosest(vector<int>& nums, int target) {
+        int res = nums[0] + nums[1] + nums[2];
+        ranges::sort(nums);
+        for (int i = 0; i < nums.size() - 2; i++) {
+            if (i > 0 && nums[i] == nums[i - 1]) {
+                continue;
+            }
+            int left = i + 1, right = nums.size() - 1;
+            while (left < right) {
+                int sum = nums[i] + nums[left] + nums[right];
+                if (sum == target) {
+                    return sum;
+                }
+                if (abs(sum - target) < abs(res - target)) {
+                    res = sum;
+                }
+                if (sum < target) {
+                    left++;
+                } else {
+                    right--;
+                }
+            }
+        }
+
+        return res;
+    }
+};
+
+void test() {
+    Solution s;
+    vector<int> nums = {-1, 2, 1, -4};
+    assert(s.threeSumClosest(nums, 1) == 2);
+    nums = {0, 0, 0};
+    assert(s.threeSumClosest(nums, 1) == 0);
+}
+
+int main() {
+    test();
+    return 0;
+}