0259-3sum-smaller

0259-3sum-smaller.playground/Contents.swift

@@ -0,0 +1,34 @@
+/// 259. 3Sum Smaller
+/// Given an array of n integers nums and a target, find the number of index triplets i, j, k
+/// with 0 <= i < j < k < n that satisfy the condition nums[i] + nums[j] + nums[k] < target.
+
+import XCTest
+
+/// Approach: Two Pointers
+func threeSumSmaller(_ nums: [Int], _ target: Int) -> Int {
+    guard nums.count > 2 else { return 0 }
+    let nums = nums.sorted()
+    var count = 0
+    for i in 0..<nums.count - 2 {
+        var j = i + 1
+        var k = nums.count - 1
+        while j < k {
+            if nums[i] + nums[j] + nums[k] < target {
+                count += k - j
+                j += 1
+            } else {
+                k -= 1
+            }
+        }
+    }
+    return count
+}
+
+class Tests: XCTestCase {
+    func testExample() {
+        let nums = [-2, 0, 1, 3]
+        XCTAssertEqual(threeSumSmaller(nums, 2), 2)
+    }
+}
+
+Tests.defaultTestSuite.run()

0259-3sum-smaller.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos' executeOnSourceChanges='false'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

README.md

@@ -56,6 +56,7 @@ You can visit the pages below to search problems by company tags. Then come back
 84 | [Largest Rectangle in Histogram](https://leetcode.com/problems/largest-rectangle-in-histogram/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/0084-largest-rectangle-in-histogram.playground/Contents.swift) | Stack
 163 | [Missing Ranges](https://leetcode.com/problems/missing-ranges/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/0163-missing-ranges.playground/Contents.swift) | Iteration
 200 | [Number of Islands](https://leetcode.com/problems/number-of-islands/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/0200-number-of-islands.playground/Contents.swift) | BFS
+259 | [Three Sum Smaller](https://leetcode.com/problems/3sum-smaller/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/0259-3sum-smaller.playground/Contents.swift) | BFS
 482 | [License Key Formatting](https://leetcode.com/problems/license-key-formatting/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/0482-license-key-formatting.playground/Contents.swift) | String
 681 | [Next Closest Time](https://leetcode.com/problems/next-closest-time/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/0681-next-closest-time.playground/Contents.swift) | Simulation
 683 | [K Empty Slots](https://leetcode.com/problems/k-empty-slots/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/0683-k-empty-slots.playground/Contents.swift) | Sliding Window