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Implemented 'Maximum Count of Positive Integer and Negative Integer' …
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LeetCode/LeetCode/Challenges/MaximumCountOfPositiveIntegerAndNegativeInteger.swift
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,79 @@ | ||
| // | ||
| // MaximumCountOfPositiveIntegerAndNegativeInteger.swift | ||
| // LeetCode | ||
| // | ||
| // Created by William Boles on 25/02/2024. | ||
| // | ||
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| import Foundation | ||
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| //https://leetcode.com/problems/maximum-count-of-positive-integer-and-negative-integer/ | ||
| struct MaximumCountOfPositiveIntegerAndNegativeInteger { | ||
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| //Time: O(log n) where n is the number of elements in `nums` | ||
| //Space: O(1) | ||
| //array | ||
| //binary search | ||
| // | ||
| //Solution Description: | ||
| //As `nums` is already sorted we can use two binary searches to find the total number negative and positive elements. First we | ||
| //use binary search to find the right-most negative element (if it exists) and return the count of negative elements. Then we | ||
| //use binary search to find the left-most positive element (if it exists) and return the count of positive elements. Next we | ||
| //take the maximum of those two values and return it. | ||
| // | ||
| //N.B. 0 does not count as negative or positive. | ||
| func maximumCount(_ nums: [Int]) -> Int { | ||
| let negativeCount = negativeElementsBinarySearch(nums) | ||
| let positiveCount = positiveElementsBinarySearch(nums) | ||
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| return max(negativeCount, positiveCount) | ||
| } | ||
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| private func negativeElementsBinarySearch(_ values: [Int]) -> Int { | ||
| let target = -1 | ||
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| var left = 0 | ||
| var right = values.count - 1 | ||
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| var result = -1 | ||
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| while left <= right { | ||
| let mid = left + (right - left) / 2 //to avoid overflow | ||
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| if values[mid] <= target { | ||
| left = mid + 1 | ||
| result = mid | ||
| } else { | ||
| right = mid - 1 | ||
| } | ||
| } | ||
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| return result + 1 //return count of negative elements | ||
| } | ||
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| private func positiveElementsBinarySearch(_ values: [Int]) -> Int { | ||
| let target = 1 | ||
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| var left = 0 | ||
| var right = values.count - 1 | ||
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| var result = -1 | ||
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| while left <= right { | ||
| let mid = left + (right - left) / 2 //to avoid overflow | ||
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| if values[mid] >= target { | ||
| right = mid - 1 | ||
| result = mid | ||
| } else { | ||
| left = mid + 1 | ||
| } | ||
| } | ||
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| guard result != -1 else { | ||
| return 0 | ||
| } | ||
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| return values.count - result | ||
| } | ||
| } |
39 changes: 39 additions & 0 deletions
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LeetCode/LeetCodeTests/Tests/MaximumCountOfPositiveIntegerAndNegativeIntegerTests.swift
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,39 @@ | ||
| // | ||
| // MaximumCountOfPositiveIntegerAndNegativeIntegerTests.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 MaximumCountOfPositiveIntegerAndNegativeIntegerTests: XCTestCase { | ||
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| //MARK: - Tests | ||
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| func test_A() { | ||
| let nums = [-2,-1,-1,1,2,3] | ||
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| let result = MaximumCountOfPositiveIntegerAndNegativeInteger().maximumCount(nums) | ||
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| XCTAssertEqual(result, 3) | ||
| } | ||
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| func test_B() { | ||
| let nums = [-3,-2,-1,0,0,1,2] | ||
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| let result = MaximumCountOfPositiveIntegerAndNegativeInteger().maximumCount(nums) | ||
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| XCTAssertEqual(result, 3) | ||
| } | ||
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| func test_C() { | ||
| let nums = [5,20,66,1314] | ||
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| let result = MaximumCountOfPositiveIntegerAndNegativeInteger().maximumCount(nums) | ||
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| XCTAssertEqual(result, 4) | ||
| } | ||
| } |