3Sum.

Author: recherst

Medium/15.3Sum.playground/Contents.swift

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+/**
+ Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0.
+
+ Notice that the solution set must not contain duplicate triplets.
+
+  
+
+ Example 1:
+ Input: nums = [-1,0,1,2,-1,-4]
+ Output: [[-1,-1,2],[-1,0,1]]
+ Explanation:
+ nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0.
+ nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0.
+ nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0.
+ The distinct triplets are [-1,0,1] and [-1,-1,2].
+ Notice that the order of the output and the order of the triplets does not matter.
+ 
+ Example 2:
+ Input: nums = [0,1,1]
+ Output: []
+ Explanation: The only possible triplet does not sum up to 0.
+ 
+ Example 3:
+ Input: nums = [0,0,0]
+ Output: [[0,0,0]]
+ Explanation: The only possible triplet sums up to 0.
+  
+
+ Constraints:
+ - 3 <= nums.length <= 3000
+ - -10^5 <= nums[i] <= 10^5
+ */
+class Solution {
+    func threeSum(_ nums: [Int]) -> [[Int]] {
+        var res: [[Int]] = []
+        let sortedNums = nums.sorted(by: <)
+        for i in 0..<sortedNums.count {
+            if sortedNums[i] > 0 {
+                break
+            }
+            // Remove duplicate element.
+            if i > 0 && sortedNums[i] == sortedNums[i - 1] {
+                continue
+            }
+            var left = i + 1
+            var right = sortedNums.count - 1
+            while left < right {
+                if sortedNums[i] + sortedNums[left] + sortedNums[right] == 0 {
+                    res.append([sortedNums[i], sortedNums[left], sortedNums[right]])
+                    
+                    // Remove duplicate element.
+                    while left < right && sortedNums[right] == sortedNums[right - 1] {
+                        right -= 1
+                    }
+                    while left < right && sortedNums[left] == sortedNums[left + 1] {
+                        left += 1
+                    }
+                    
+                    left += 1
+                    right -= 1
+                } else if sortedNums[i] + sortedNums[left] + sortedNums[right] > 0 {
+                    right -= 1
+                } else {
+                    left += 1
+                }
+            }
+        }
+        return res
+    }
+}
+
+let s = Solution()
+let r = s.threeSum([-1,0,1,2,-1,-4])
+print(r)

Medium/15.3Sum.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='ios' buildActiveScheme='true' importAppTypes='true'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Medium/15.3Sum.playground/playground.xcworkspace/contents.xcworkspacedata

@@ -113,4 +113,4 @@
 6. [String to Integer (atoi)](https://github.com/recherst/leetcode-algtorithm/blob/main/Medium/8.String%20to%20Integer%20(atoi).playground/Contents.swift)
 7. [Container With Most Water](https://github.com/recherst/leetcode-algtorithm/blob/main/Medium/11.Container%20With%20Most%20Water.playground/Contents.swift)
 8. [Integer to Roman](https://github.com/recherst/leetcode-algtorithm/blob/main/Medium/12.Integer%20to%20Roman.playground/Contents.swift)
-
+9. [3Sum](https://github.com/recherst/leetcode-algtorithm/blob/main/Medium/15.3Sum.playground/Contents.swift)