Array partition.

Author: recherst

Easy/39.Combination Sum.playground/Contents.swift

@@ -0,0 +1,56 @@
+/**
+ Given an array of distinct integers candidates and a target integer target, return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order.
+
+ The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different.
+
+ It is guaranteed that the number of unique combinations that sum up to target is less than 150 combinations for the given input.
+
+  
+
+ Example 1:
+ Input: candidates = [2,3,6,7], target = 7
+ Output: [[2,2,3],[7]]
+ Explanation:
+ 2 and 3 are candidates, and 2 + 2 + 3 = 7. Note that 2 can be used multiple times.
+ 7 is a candidate, and 7 = 7.
+ These are the only two combinations.
+ 
+ Example 2:
+ Input: candidates = [2,3,5], target = 8
+ Output: [[2,2,2,2],[2,3,3],[3,5]]
+ 
+ Example 3:
+ Input: candidates = [2], target = 1
+ Output: []
+  
+
+ Constraints:
+ - 1 <= candidates.length <= 30
+ - 1 <= candidates[i] <= 200
+ - All elements of candidates are distinct.
+ - 1 <= target <= 500
+ */
+class Solution {
+    func combinationSum(_ candidates: [Int], _ target: Int) -> [[Int]] {
+        let sortedCandidates = candidates.sorted(by: <)
+        var result = [[Int]]()
+        for element in candidates {
+            if element == target {
+                result.append([target])
+                break
+            }
+            if element > target {
+                break
+            }
+            if target % element == 0 {
+                let times = target / element
+                var arr = [Int]()
+                for i in 0..<times {
+                    arr.append(element)
+                }
+                result.append(arr)
+            }
+        }
+        return result
+    }
+}

Easy/39.Combination Sum.playground/contents.xcplayground

@@ -0,0 +1,4 @@
+<?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>

Easy/39.Combination Sum.playground/playground.xcworkspace/contents.xcworkspacedata

@@ -0,0 +1,41 @@
+/**
+ Given an integer array nums of 2n integers, group these integers into n pairs (a1, b1), (a2, b2), ..., (an, bn) such that the sum of min(ai, bi) for all i is maximized. Return the maximized sum.
+
+  
+
+ Example 1:
+ Input: nums = [1,4,3,2]
+ Output: 4
+ Explanation: All possible pairings (ignoring the ordering of elements) are:
+ 1. (1, 4), (2, 3) -> min(1, 4) + min(2, 3) = 1 + 2 = 3
+ 2. (1, 3), (2, 4) -> min(1, 3) + min(2, 4) = 1 + 2 = 3
+ 3. (1, 2), (3, 4) -> min(1, 2) + min(3, 4) = 1 + 3 = 4
+ So the maximum possible sum is 4.
+ 
+ Example 2:
+ Input: nums = [6,2,6,5,1,2]
+ Output: 9
+ Explanation: The optimal pairing is (2, 1), (2, 5), (6, 6). min(2, 1) + min(2, 5) + min(6, 6) = 1 + 2 + 6 = 9.
+  
+
+ Constraints:
+ - 1 <= n <= 104
+ - nums.length == 2 * n
+ - -104 <= nums[i] <= 104
+ */
+class Solution {
+    func arrayPairSum(_ nums: [Int]) -> Int {
+        let sortedNums = nums.sorted(by: <)
+        var i = 0
+        var sum = 0
+        while i <= nums.count - 2 {
+            sum += sortedNums[i]
+            i += 2
+        }
+        return sum
+    }
+}
+
+let s = Solution()
+let r = s.arrayPairSum([6,2,6,5,1,2])
+print(r)

Easy/561.Array Partition.playground/Contents.swift

@@ -0,0 +1,4 @@
+<?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>

Easy/561.Array Partition.playground/contents.xcplayground

@@ -32,7 +32,6 @@
  */
 class Solution {
     func countAndSay(_ n: Int) -> String {
-        if n == 1 { return "1" }
         var sumArr = ["1"]
         var count = 0
         var number = Character("1")
@@ -65,5 +64,5 @@ class Solution {
 }
 
 let s = Solution()
-let r = s.countAndSay(30)
+let r = s.countAndSay(1)
 print(r)

Easy/561.Array Partition.playground/playground.xcworkspace/contents.xcworkspacedata

@@ -110,6 +110,7 @@
 106. [Student Attendance Record I](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/551.Student%20Attendance%20Record%20I.playground/Contents.swift)
 107. [Reverse Words in a String III](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/557.Reverse%20Words%20in%20a%20String%20III.playground/Contents.swift)
 108. [Maximum Depth of N-ary Tree](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/559.Maximum%20Depth%20of%20N-ary%20Tree.playground/Contents.swift)
+109. [Array Partition](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/561.Array%20Partition.playground/Contents.swift)
 
 #### Medium