From 995aa86ab2eb21559bcdd0d3cc91e486e33cade1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=9E=81=E5=AE=A2=E5=AD=A6=E4=BC=9F?= <qxuwei@yeah.net>
Date: Wed, 8 Sep 2021 13:28:04 +0800
Subject: [PATCH] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=20=E7=AC=AC18=E9=A2=98.=20?=
 =?UTF-8?q?=E5=9B=9B=E6=95=B0=E4=B9=8B=E5=92=8C=20Swift=E7=89=88=E6=9C=AC?=
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---
 problems/0018.四数之和.md | 48 +++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/problems/0018.四数之和.md b/problems/0018.四数之和.md
index c81c5df7..9891f0fe 100644
--- a/problems/0018.四数之和.md
+++ b/problems/0018.四数之和.md
@@ -354,6 +354,54 @@ class Solution {
 }
 ```
 
+Swift:
+```swift
+func fourSum(_ nums: [Int], _ target: Int) -> [[Int]] {
+    var res = [[Int]]()
+    var sorted = nums
+    sorted.sort()
+    for k in 0 ..< sorted.count {
+        // 这种剪枝不行,target可能是负数
+//            if sorted[k] > target {
+//                return res
+//            }
+        // 去重
+        if k > 0 && sorted[k] == sorted[k - 1] {
+            continue
+        }
+        
+        let target2 = target - sorted[k]
+        for i in (k + 1) ..< sorted.count {
+            if i > (k + 1) && sorted[i] == sorted[i - 1] {
+                continue
+            }
+            var left = i + 1
+            var right = sorted.count - 1
+            while left < right {
+                let sum = sorted[i] + sorted[left] + sorted[right]
+                if sum < target2 {
+                    left += 1
+                } else if sum > target2 {
+                    right -= 1
+                } else {
+                    res.append([sorted[k], sorted[i], sorted[left], sorted[right]])
+                    while left < right && sorted[left] == sorted[left + 1] {
+                        left += 1
+                    }
+                    while left < right && sorted[right] == sorted[right - 1]  {
+                        right -= 1
+                    }
+                    // 找到答案 双指针同时收缩
+                    left += 1
+                    right -= 1
+                }
+            }
+        }
+    }
+    return res
+}
+```
+
 -----------------------
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