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Implemented 'Find Target Indices After Sorting Array' challenge
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81 changes: 81 additions & 0 deletions
81
LeetCode/LeetCode/Challenges/FindTargetIndicesAfterSortingArray.swift
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,81 @@ | ||
| // | ||
| // FindTargetIndicesAfterSortingArray.swift | ||
| // LeetCode | ||
| // | ||
| // Created by William Boles on 25/02/2024. | ||
| // | ||
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| import Foundation | ||
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| //https://leetcode.com/problems/find-target-indices-after-sorting-array/ | ||
| struct FindTargetIndicesAfterSortingArray { | ||
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| //Time: O(n log n) where n is the number of elements in `nums` | ||
| //Space: O(n) | ||
| //array | ||
| //sorting | ||
| //binary search | ||
| // | ||
| //Solution Description: | ||
| //With a sorted array of `nums` we can perform two binary searches to find the first occurrence of `target` and the last | ||
| //occurrence. With these two indexes we can construct the result array from that range. | ||
| // | ||
| //N.B. Both `leftMostIndex` and `rightMostIndex` might have the same index value or they both might be nil but one can't | ||
| //be nil while the other is non-nil. | ||
| func targetIndices(_ nums: [Int], _ target: Int) -> [Int] { | ||
| let sortedNums = nums.sorted(by: <) | ||
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| let leftMostIndex = firstOccurrence(sortedNums, target) | ||
| let rightMostIndex = lastOccurrence(sortedNums, target) | ||
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| guard let leftMostIndex = leftMostIndex, let rightMostIndex = rightMostIndex else { | ||
| return [Int]() | ||
| } | ||
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| return Array(leftMostIndex...rightMostIndex) | ||
| } | ||
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| private func firstOccurrence(_ values: [Int], _ target: Int) -> Int? { | ||
| var left = 0 | ||
| var right = values.count - 1 | ||
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| var result: Int? | ||
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| while left <= right { | ||
| let mid = left + (right - left) / 2 //to avoid overflow | ||
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| if values[mid] == target { | ||
| result = mid | ||
| right = mid - 1 | ||
| } else if values[mid] > target { | ||
| right = mid - 1 | ||
| } else { | ||
| left = mid + 1 | ||
| } | ||
| } | ||
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| return result | ||
| } | ||
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| private func lastOccurrence(_ values: [Int], _ target: Int) -> Int? { | ||
| var left = 0 | ||
| var right = values.count - 1 | ||
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| var result: Int? | ||
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| while left <= right { | ||
| let mid = left + (right - left) / 2 //to avoid overflow | ||
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| if values[mid] == target { | ||
| result = mid | ||
| left = mid + 1 | ||
| } else if values[mid] < target { | ||
| left = mid + 1 | ||
| } else { | ||
| right = mid - 1 | ||
| } | ||
| } | ||
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| return result | ||
| } | ||
| } |
69 changes: 69 additions & 0 deletions
69
LeetCode/LeetCodeTests/Tests/FindTargetIndicesAfterSortingArrayTests.swift
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,69 @@ | ||
| // | ||
| // FindTargetIndicesAfterSortingArrayTests.swift | ||
| // LeetCodeTests | ||
| // | ||
| // Created by William Boles on 25/02/2024. | ||
| // | ||
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| import XCTest | ||
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| @testable import LeetCode | ||
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| final class FindTargetIndicesAfterSortingArrayTests: XCTestCase { | ||
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| //MARK: - Tests | ||
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| func test_A() { | ||
| let nums = [1,2,5,2,3] | ||
| let target = 2 | ||
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| let result = FindTargetIndicesAfterSortingArray().targetIndices(nums, target) | ||
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| XCTAssertEqual(result, [1,2]) | ||
| } | ||
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| func test_B() { | ||
| let nums = [1,2,5,2,3] | ||
| let target = 3 | ||
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| let result = FindTargetIndicesAfterSortingArray().targetIndices(nums, target) | ||
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| XCTAssertEqual(result, [3]) | ||
| } | ||
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| func test_C() { | ||
| let nums = [1,2,5,2,3] | ||
| let target = 5 | ||
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| let result = FindTargetIndicesAfterSortingArray().targetIndices(nums, target) | ||
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| XCTAssertEqual(result, [4]) | ||
| } | ||
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| func test_D() { | ||
| let nums = [1,2,5,2,3] | ||
| let target = 7 | ||
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| let result = FindTargetIndicesAfterSortingArray().targetIndices(nums, target) | ||
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| XCTAssertEqual(result, [Int]()) | ||
| } | ||
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| func test_E() { | ||
| let nums = [48,90,9,21,31,35,19,69,29,52,100,54,21,86,6,45,42,5,62,77,15,38] | ||
| let target = 6 | ||
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| let result = FindTargetIndicesAfterSortingArray().targetIndices(nums, target) | ||
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| XCTAssertEqual(result, [1]) | ||
| } | ||
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| func test_F() { | ||
| let nums = [19,35,87,45,93,10,79,41,57,75,66,56,74,25,59,71,19,18,84,28,32,63,73,97,53] | ||
| let target = 8 | ||
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| let result = FindTargetIndicesAfterSortingArray().targetIndices(nums, target) | ||
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| XCTAssertEqual(result, [Int]()) | ||
| } | ||
| } |