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Author: lzl124631x

leetcode/16. 3Sum Closest/README.md

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+# [16. 3Sum Closest (Medium)](https://leetcode.com/problems/3sum-closest/submissions/)
+
+<p>Given an array <code>nums</code> of <em>n</em> integers and an integer <code>target</code>, find three integers in <code>nums</code>&nbsp;such that the sum is closest to&nbsp;<code>target</code>. Return the sum of the three integers. You may assume that each input would have exactly one solution.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre><strong>Input:</strong> nums = [-1,2,1,-4], target = 1
+<strong>Output:</strong> 2
+<strong>Explanation:</strong> The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>3 &lt;= nums.length &lt;= 10^3</code></li>
+	<li><code>-10^3&nbsp;&lt;= nums[i]&nbsp;&lt;= 10^3</code></li>
+	<li><code>-10^4&nbsp;&lt;= target&nbsp;&lt;= 10^4</code></li>
+</ul>
+
+
+**Related Topics**:  
+[Array](https://leetcode.com/tag/array/), [Two Pointers](https://leetcode.com/tag/two-pointers/)
+
+**Similar Questions**:
+* [3Sum (Medium)](https://leetcode.com/problems/3sum/)
+* [3Sum Smaller (Medium)](https://leetcode.com/problems/3sum-smaller/)
+
+## Solution 1.
+
+```cpp
+// OJ: https://leetcode.com/problems/3sum-closest/
+// Author: github.com/lzl124631x
+// Time: O(N^2)
+// Space: O(1)
+class Solution {
+public:
+    int threeSumClosest(vector<int>& A, int target) {
+        sort(begin(A), end(A));
+        int diff = INT_MAX;
+        for (int i = 0, N = A.size(); i < N; ++i) {
+            int L = i + 1, R = N - 1;
+            while (L < R) {
+                int sum = A[L] + A[R] + A[i];
+                if (sum == target) return target;
+                if (abs(target - sum) < abs(diff)) diff = target - sum;
+                if (sum > target) --R;
+                else ++L;
+            }
+        }
+        return target - diff;
+    }
+};
+```