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[Swift]LeetCode16. 最接近的三数之和 | 3Sum Closest

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➤微信公众号：山青咏芝（shanqingyongzhi）
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➤原文地址：https://www.cnblogs.com/strengthen/p/9885069.html
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Given an array nums of n integers and an integer target, find three integers in nums such that the sum is closest to target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

Example:

Given array nums = [-1, 2, 1, -4], and target = 1.
The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

给定一个包括 n 个整数的数组 nums 和一个目标值 target。找出 nums 中的三个整数，使得它们的和与 target 最接近。返回这三个数的和。假定每组输入只存在唯一答案。

例如，给定数组 nums = [-1，2，1，-4], 和 target = 1.
与 target 最接近的三个数的和为 2. (-1 + 2 + 1 = 2).

24ms

 1 class Solution {
 2     func threeSumClosest(_ nums: [Int], _ target: Int) -> Int {
 3         if (nums.count < 3) {
 4             return 0
 5         }
 6         var result = Int.max
 7         var sortedNums = nums.sorted(by: <)
 8         for index in 0..<(nums.count - 2) {
 9             if index == 0 || sortedNums[index] != sortedNums[index - 1] {
10                 var firstNum = sortedNums[index]
11                 var startIndex = index + 1
12                 var endIndex = nums.count - 1
13                 while(startIndex < endIndex) {
14                     var temp = firstNum + sortedNums[startIndex] + sortedNums[endIndex]
15                     
16                     if (result == Int.max || abs(temp - target) < abs(result - target)) {
17                         result = temp
18                     }
19                     if (temp > target) {
20                             endIndex -= 1
21                     } else if (temp < target) {
22                             startIndex += 1
23                     } else {
24                         return temp
25                     }
26                 }
27             }
28         }
29         return result
30     }
31 }

24ms

 1 class Solution {
 2     func threeSumClosest(_ nums: [Int], _ target: Int) -> Int {
 3         if(nums.count < 3){
 4             var result = 0
 5             for value in nums {
 6                 result = result + value
 7             }
 8             return result;
 9         }
10         var tempNums = nums.sorted{$0<$1}
11         let count = tempNums.count
12         var threeSum = tempNums[0] + tempNums[1] + tempNums[2]
13         // print(tempNums)
14         for indexF in 0 ..< count {
15             if (indexF != 0) && (tempNums[indexF] == tempNums[indexF - 1]){
16                 continue
17             }
18             let tempArray = self.aFunction(numbers: tempNums, begin: indexF + 1, end: count)
19             //            print(tempArray)
20             var left:Int = 0
21             var right:Int = tempArray.count - 1
22             while left < right {
23                 // print(threeSum)
24                 var newOffsetValue = tempArray[left] + tempArray[right] + tempNums[indexF] - target
25                 
26                 if(newOffsetValue == 0){
27                     return target;
28                 }
29                 
30                 if(threeSum - target < 0){
31                     if(newOffsetValue < 0){
32                         if(newOffsetValue + target > threeSum){
33                             threeSum = tempArray[left] + tempArray[right] + tempNums[indexF]
34                             left = left + 1
35                         }else{
36                             left = left + 1
37                         }
38                     }else{
39                         if(abs(newOffsetValue) < abs(threeSum - target)){
40                             threeSum = tempArray[left] + tempArray[right] + tempNums[indexF]
41                             right = right - 1
42                         }else{
43                             right = right - 1
44                         }
45                     }
46                 }else{
47                     if(newOffsetValue < 0){
48                         if(abs(newOffsetValue) < abs(threeSum - target)){
49                             threeSum = tempArray[left] + tempArray[right] + tempNums[indexF]
50                             left = left + 1
51                         }else{
52                             left = left + 1
53                         }
54                     }else{
55                         if(newOffsetValue + target  < threeSum){
56                             threeSum = tempArray[left] + tempArray[right] + tempNums[indexF]
57                             right = right - 1
58                         }else{
59                             right = right - 1
60                         }
61                     }
62                 }
63             }
64         }
65         return threeSum
66     }
67     
68     
69     func aFunction(numbers: Array<Int>, begin: Int, end: Int) -> Array<Int> {
70         let newNumbers = Array(numbers[begin..<end])
71         return newNumbers
72     }
73     
74 }

28ms

 1 class Solution {
 2     func threeSumClosest(_ nums: [Int], _ target: Int) -> Int {
 3         let count = nums.count 
 4         guard count > 2 else { return 0 }
 5         let nums = nums.sorted()
 6         
 7         var close = Int.max
 8         for i in 0..<count - 2 {
 9             if i > 0 && nums[i] == nums[i - 1] {
10                 continue
11             }
12             
13             var twoSum = target - nums[i]
14             var left = i + 1, right = count - 1
15             
16             while left < right {
17                 if twoSum == nums[left] + nums[right] {
18                     return target
19                 } else if twoSum > nums[left] + nums[right] {
20                     if twoSum - nums[left] - nums[right] < abs(close) {
21                         close = twoSum - nums[left] - nums[right]
22                     }
23                     left += 1
24                 } else {
25                     if nums[left] + nums[right] - twoSum < abs(close) {
26                         close = twoSum - nums[left] - nums[right]
27                     }
28                     right -= 1
29                 }
30             }
31             
32             
33         }
34         
35         return target - close
36     }
37 }

32ms

 1 class Solution {
 2     func threeSumClosest(_ nums: [Int], _ target: Int) -> Int {
 3         guard nums.count > 2 else { return 0 }
 4         
 5         var finalSum = nums[0] + nums[1] + nums[2]
 6         var nums = nums.sorted(){$0 < $1}
 7         for i in 0..<nums.count - 2 {
 8             var j = i + 1, k = nums.count - 1
 9             while j < k {
10                 var currSum = nums[i] + nums[j] + nums[k] 
11                 if currSum == target {
12                     return currSum
13                 }else {
14                     if abs(target - currSum) < abs(target - finalSum) {
15                         finalSum = currSum
16                     }
17                     if currSum < target {
18                         j += 1
19                     }else {
20                         k -= 1
21                     }
22                 }
23             }
24         }
25         return finalSum
26     }
27 }

36ms

 1 class Solution {
 2     func threeSumClosest(_ nums: [Int], _ target: Int) -> Int {
 3         
 4         var sortedNums = nums.sorted()   
 5         //print(sortedNums)
 6         var closestSum = target >= 0 ? Int.max: Int.min
 7         for index1 in 0..<(nums.count-2) {
 8             var index2 = index1 + 1
 9             var index3 = nums.count - 1
10             
11             while (index2 < index3) {
12                 //print(index1, index2, index3)
13                 var sum = sortedNums[index1] + sortedNums[index2] + sortedNums[index3]
14                 if sum == target {
15                     return sum
16                 }
17                 if (abs(target - closestSum) > abs(target - sum)) {
18                     closestSum = sum
19                 }
20 
21                 //print(closestSum, target)
22                 if target < sum {
23                     index3 -= 1
24                 } else {
25                     index2 += 1
26                 }
27             }
28         }
29         return closestSum
30     }
31 }

48ms

 1 class Solution {
 2     func threeSumClosest(_ nums: [Int], _ target: Int) -> Int {
 3         var diff = Int.max
 4         var closestNum = Int.max
 5         let numsSorted = nums.sorted()
 6         let maxIndex = numsSorted.count - 1 
 7         var lastNum: Optional<Int> = nil
 8         for i in 0..<(numsSorted.count - 2) {
 9             let num = numsSorted[i]
10             if num == lastNum {
11                 continue
12             }
13             
14             var left = i + 1
15             var right = maxIndex
16             let remainder = target - num
17             while left < right {
18                 let currentDiff = remainder - numsSorted[left] - numsSorted[right]
19                 let absCurrentDiff = abs(currentDiff)
20                 if absCurrentDiff < diff {
21                     if absCurrentDiff == 0 {
22                         return target
23                     }
24                     diff = absCurrentDiff
25                     closestNum = target - currentDiff
26                 }
27                 
28                 if currentDiff > 0 {
29                     left = left + 1
30                 } else {
31                     right = right - 1
32                 }
33             }
34             
35             lastNum = num
36         }
37         
38         return closestNum
39     }
40 }

76ms

 1 class Solution {
 2     var diff = Int.max
 3     var sum = 0
 4     func threeSumClosest(_ nums: [Int], _ target: Int) -> Int {
 5         if nums.count < 3 {
 6             return 0
 7         }
 8         
 9         var nums = nums
10         nums.sort { $0 < $1 }
11         print(nums)
12         
13         for i in 0..<nums.count-2 {
14             twoSumClosest(i + 1, nums.count - 1, nums[i], nums, target - nums[i])
15         }
16         return sum
17     }
18     
19     func twoSumClosest(_ start: Int, _ end: Int, _ num: Int, _ nums: [Int], _ target: Int) {
20         var start = start
21         var end = end
22         while start < end {
23             if abs(nums[start] + nums[end] - target) < diff {
24                 sum = nums[start] + nums[end] + num
25                 diff = abs(nums[start] + nums[end] - target)
26             } 
27             
28             if nums[start] + nums[end] < target {
29                 start += 1
30             }
31             else {
32                 end -= 1
33             }
34         }
35     }
36 }

96ms

 1 class Solution {
 2     func twoSumClosest(sortedNums: [Int], beginIndex: Int, target: Int) -> Int {
 3         var minGap = Int.max
 4         var closestSum = 0
 5 
 6         var low = beginIndex
 7         var high = sortedNums.count - 1
 8 
 9 
10         while low < high {
11             let sum = sortedNums[low] + sortedNums[high]
12 
13             // 更新相关结果
14             let gap = abs(sum - target)
15             if gap < minGap {
16                 minGap = gap
17                 closestSum = sum
18             }
19 
20             // 移动下标
21             if sum < target {
22                 repeat {
23                     low += 1
24                 } while sortedNums[low] == sortedNums[low - 1] && low < high
25             } else {
26                 repeat {
27                     high -= 1
28                 } while sortedNums[high] == sortedNums[high + 1] && low < high
29             }
30         }
31 
32         return closestSum
33     }
34 
35     func threeSumClosest(_ nums: [Int], _ target: Int) -> Int {
36         guard nums.count >= 3 else { return 0 }
37         var minGap = Int.max
38         var closestSum = 0
39 
40         let sortedNums = nums.sorted()
41 
42         for i in 0..<sortedNums.count - 2 {
43             let closest2Sum = twoSumClosest(sortedNums: sortedNums, beginIndex: i + 1, target: target - sortedNums[i])
44             let sum = closest2Sum + sortedNums[i]
45             let gap = abs(target - sum)
46 
47             if gap < minGap {
48                 minGap = gap
49                 closestSum = sum
50             }
51         }
52 
53         return closestSum
54     }
55 }

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原文地址：https://www.cnblogs.com/strengthen/p/9885069.html