032-longest-valid-parentheses

Author: bofeizhu

032-longest-valid-parentheses.playground/Contents.swift

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+/// 32. Longest Valid Parentheses
+/// Given a string containing just the characters '(' and ')', find the length of the longest valid
+/// (well-formed) parentheses substring.
+
+import XCTest
+
+/// Approach: Stack
+func longestValidParentheses(_ s: String) -> Int {
+    var stack = [-1]
+    var longest = 0
+    for (idx, p) in s.enumerated() {
+        if p == "(" {
+            stack.append(idx)
+        } else {
+            stack.popLast()
+            if let last = stack.last {
+                longest = max(longest, idx - last)
+            } else {
+                stack.append(idx)
+            }
+        }
+        
+    }
+    return longest
+}
+
+class Tests: XCTestCase {
+    func testExample() {
+        XCTAssertEqual(longestValidParentheses("(()"), 2)
+    }
+}
+
+Tests.defaultTestSuite.run()

032-longest-valid-parentheses.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

@@ -47,3 +47,4 @@
 29 | [Divide Two Integers](https://leetcode.com/problems/divide-two-integers/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/029-divide-two-integers.playground/Contents.swift) | String
 30 | [Substring with Concatenation of All Words](https://leetcode.com/problems/substring-with-concatenation-of-all-words/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/030-substring-with-concatenation-of-all-words.playground/Contents.swift) | Two Pointers
 31 | [Next Permutation](https://leetcode.com/problems/next-permutation/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/031-next-permutation.playground/Contents.swift) | Two Pointers
+32 | [Longest Valid Parentheses](https://leetcode.com/problems/longest-valid-parentheses/description/) | [Solution](https://github.com/zhubofei/LeetCode-Swift/blob/master/032-longest-valid-parentheses.playground/Contents.swift) | Stack