3Sum Closest
<p>Given an integer array <code>nums</code> of length <code>n</code> and an integer <code>target</code>, find three integers in <code>nums</code> such that the sum is closest to <code>target</code>.</p>

<p>Return <em>the sum of the three integers</em>.</p>

<p>You may assume that each input would have exactly one solution.</p>

<p>&nbsp;</p>
<p><strong class="example">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><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [0,0,0], target = 1
<strong>Output:</strong> 0
<strong>Explanation:</strong> The sum that is closest to the target is 0. (0 + 0 + 0 = 0).
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>3 &lt;= nums.length &lt;= 500</code></li>
	<li><code>-1000 &lt;= nums[i] &lt;= 1000</code></li>
	<li><code>-10<sup>4</sup> &lt;= target &lt;= 10<sup>4</sup></code></li>
</ul>
Array; Two Pointers; Sorting
func threeSumClosest(nums []int, target int) int {
	sort.Ints(nums)
	ans := 1 << 30
	n := len(nums)
	for i, v := range nums {
		j, k := i+1, n-1
		for j < k {
			t := v + nums[j] + nums[k]
			if t == target {
				return t
			}
			if abs(t-target) < abs(ans-target) {
				ans = t
			}
			if t > target {
				k--
			} else {
				j++
			}
		}
	}
	return ans
}

func abs(x int) int {
	if x < 0 {
		return -x
	}
	return x
}