20. Valid Parentheses

```Solution.c bool isValid(char* s) { char stack[10000]; int top = -1; for (int i = 0; s[i]; i++) { if (s[i] == '(' || s[i] == '{' || s[i] == '[') { stack[++top] = s[i]; } else { if (top == -1) return false; char c = stack[top--]; if ((s[i] == ')' && c != '(') || (s[i] == '}' && c != '{') || (s[i] == ']' && c != '[')) { return false; } } } return top == -1; } ``` ```Solution.cpp class Solution { public: bool isValid(string s) { stack<char> stack; for (char c : s) { if (c == '(' || c == '{' || c == '[') { stack.push(c); } else { if (stack.empty()) return false; char top = stack.top(); stack.pop(); if ((c == ')' && top != '(') || (c == '}' && top != '{') || (c == ']' && top != '[')) { return false; } } } return stack.empty(); } }; ``` ```Solution.cs public class Solution { public bool IsValid(string s) { Stack<char> stack = new Stack<char>(); foreach (char c in s) { if (c == '(' || c == '{' || c == '[') { stack.Push(c); } else { if (stack.Count == 0) return false; char top = stack.Pop(); if ((c == ')' && top != '(') || (c == '}' && top != '{') || (c == ']' && top != '[')) { return false; } } } return stack.Count == 0; } } ``` ```Solution.dart class Solution { bool isValid(String s) { List<String> stack = []; for (var c in s.split('')) { if (c == '(' || c == '{' || c == '[') { stack.add(c); } else { if (stack.isEmpty) return false; var top = stack.removeLast(); if ((c == ')' && top != '(') || (c == '}' && top != '{') || (c == ']' && top != '[')) { return false; } } } return stack.isEmpty; } } ``` ```Solution.erl -spec is_valid(S :: unicode:unicode_binary()) -> boolean(). is_valid(S) -> Chars = unicode:characters_to_list(S), Pairs = #{ $) => $(, $] => $[, $} => ${ }, check(Chars, [], Pairs). check([], [], _Pairs) -> true; check([], _Stack, _Pairs) -> false; check([C | Rest], Stack, Pairs) -> case maps:get(C, Pairs, undefined) of undefined -> check(Rest, [C | Stack], Pairs); Open -> case Stack of [Open | Tail] -> check(Rest, Tail, Pairs); _ -> false end end. ``` ```Solution.ex defmodule Solution do @SPEC is_valid(s :: String.t) :: boolean def is_valid(s), do: match_brackets(s, []) defp match_brackets(<<?(, rest::binary>>, stack), do: match_brackets(rest, [?( | stack]) defp match_brackets(<<?[, rest::binary>>, stack), do: match_brackets(rest, [?[ | stack]) defp match_brackets(<<?{, rest::binary>>, stack), do: match_brackets(rest, [?{ | stack]) defp match_brackets(<<?), rest::binary>>, [?( | stack]), do: match_brackets(rest, stack) defp match_brackets(<<?], rest::binary>>, [?[ | stack]), do: match_brackets(rest, stack) defp match_brackets(<<?}, rest::binary>>, [?{ | stack]), do: match_brackets(rest, stack) defp match_brackets("", []), do: true defp match_brackets(_, _), do: false end ``` ```Solution.go func isValid(s string) bool { stack := []rune{} for _, c := range s { if c == '(' || c == '{' || c == '[' { stack = append(stack, c) } else { if len(stack) == 0 { return false } top := stack[len(stack)-1] stack = stack[:len(stack)-1] if (c == ')' && top != '(') || (c == '}' && top != '{') || (c == ']' && top != '[') { return false } } } return len(stack) == 0 } ``` ```Solution.java class Solution { public boolean isValid(String s) { Stack<Character> stack = new Stack<>(); for (char c : s.toCharArray()) { if (c == '(' || c == '{' || c == '[') { stack.push(c); } else { if (stack.isEmpty()) return false; char top = stack.pop(); if ((c == ')' && top != '(') || (c == '}' && top != '{') || (c == ']' && top != '[')) { return false; } } } return stack.isEmpty(); } } ``` ```Solution.js /** * @param {string} s * @return {boolean} */ var isValid = function(s) { const stack = []; for (const c of s) { if (c === '(' || c === '{' || c === '[') { stack.push(c); } else { if (stack.length === 0) return false; const top = stack.pop(); if ((c === ')' && top !== '(') || (c === '}' && top !== '{') || (c === ']' && top !== '[')) { return false; } } } return stack.length === 0; }; ``` ```Solution.kt class Solution { fun isValid(s: String): Boolean { val stack = mutableListOf<Char>() for (c in s) { if (c == '(' || c == '{' || c == '[') { stack.add(c) } else { if (stack.isEmpty()) return false val top = stack.removeAt(stack.size - 1) if ((c == ')' && top != '(') || (c == '}' && top != '{') || (c == ']' && top != '[')) { return false } } } return stack.isEmpty() } } ``` ```Solution.php class Solution { /** * @param String $s * @return Boolean */ function isValid($s) { $stack = []; foreach (str_split($s) as $c) { if ($c == '(' || $c == '{' || $c == '[') { array_push($stack, $c); } else { if (empty($stack)) return false; $top = array_pop($stack); if (($c == ')' && $top != '(') || ($c == '}' && $top != '{') || ($c == ']' && $top != '[')) { return false; } } } return empty($stack); } } ``` ```Solution.py class Solution: def isValid(self, s: str) -> bool: stack = [] for c in s: if c in '({[': stack.append(c) else: if not stack: return False top = stack.pop() if (c == ')' and top != '(') or \ (c == '}' and top != '{') or \ (c == ']' and top != '['): return False return len(stack) == 0 ``` ```Solution.rb # @param {String} s # @return {Boolean} def is_valid(s) stack = [] s.each_char do |c| if c == '(' || c == '{' || c == '[' stack.push(c) else return false if stack.empty? top = stack.pop return false if (c == ')' && top != '(') || (c == '}' && top != '{') || (c == ']' && top != '[') end end stack.empty? end ``` ```Solution.rkt (define is-valid (lambda (s) (let ([pairs (make-hash)]) (hash-set! pairs #\) #\() (hash-set! pairs #\] #\[) (hash-set! pairs #\} #\{) (let loop ([chars (string->list s)] [stack '()]) (cond [(null? chars) (null? stack)] [else (define ch (car chars)) (cond [(member ch (list #\( #\[ #\{)) (loop (cdr chars) (cons ch stack))] [(hash-has-key? pairs ch) (and (not (null? stack)) (equal? (hash-ref pairs ch) (car stack)) (loop (cdr chars) (cdr stack)))] [else #f])]))))) (provide is-valid) ``` ```Solution.rs impl Solution { pub fn is_valid(s: String) -> bool { let mut stack = Vec::new(); for c in s.chars() { if c == '(' || c == '{' || c == '[' { stack.push(c); } else { if stack.is_empty() { return false; } let top = stack.pop().unwrap(); if (c == ')' && top != '(') || (c == '}' && top != '{') || (c == ']' && top != '[') { return false; } } } stack.is_empty() } } ``` ```Solution.scala object Solution { import scala.collection.mutable def isValid(s: String): Boolean = { val stack = new Array[Char](s.length) val openBrackets = "({[" var result = true var index = 0 var stackIndex = 0 while (index < s.length && result) { val currentBracket = s.charAt(index) if(currentBracket == '(') { stack(stackIndex) = ')' stackIndex += 1 } else if (currentBracket == '{') { stack(stackIndex) = '}' stackIndex += 1 } else if (currentBracket == '[') { stack(stackIndex) = ']' stackIndex += 1 } else if(stackIndex > 0 && stack(stackIndex-1) == currentBracket) { stackIndex -= 1 } else { result = false } index += 1 } stackIndex == 0 && result } } ``` ```Solution.swift class Solution { func isValid(_ s: String) -> Bool { var stack: [Character] = [] for c in s { if c == "(" || c == "{" || c == "[" { stack.append(c) } else { if stack.isEmpty { return false } let top = stack.removeLast() if (c == ")" && top != "(") || (c == "}" && top != "{") || (c == "]" && top != "[") { return false } } } return stack.isEmpty } } ``` ```Solution.ts function isValid(s: string): boolean { const stack: string[] = []; for (const c of s) { if (c === '(' || c === '{' || c === '[') { stack.push(c); } else { if (stack.length === 0) return false; const top = stack.pop(); if ((c === ')' && top !== '(') || (c === '}' && top !== '{') || (c === ']' && top !== '[')) { return false; } } } return stack.length === 0; } ```

Author: nendroids

sol/solution/0001-0100/0020/README.md

@@ -0,0 +1,42 @@
+# [**20. Valid Parentheses**](https://leetcode.com/problems/valid-parentheses/description/)
+
+Given a string `s` containing just the characters `'('`, `')'`, `'{'`, `'}'`, `'['` and `']'`, determine if the input string is valid.
+
+An input string is valid if:
+1. Open brackets must be closed by the same type of brackets.
+2. Open brackets must be closed in the correct order.
+3. Every close bracket has a corresponding open bracket of the same type.
+
+#### **Example 1:**
+```md
+Input: s = "()"
+Output: true
+```
+
+#### **Example 2:**
+```md
+Input: s = "()[]{}"
+Output: true
+```
+
+#### **Example 3:**
+```md
+Input: s = "(]"
+Output: false
+```
+
+#### **Example 4:**
+```md
+Input: s = "([])"
+Output: true
+```
+
+#### **Example 5:**
+```md
+Input: s = "([)]"
+Output: false
+```
+
+#### **Constraints:**
+> - `1 <= s.length <= 10⁴`
+> - `s` consists of parentheses only `'()[]{}'`.

sol/solution/0001-0100/0020/Solution.c

@@ -0,0 +1,18 @@
+bool isValid(char* s) {
+ char stack[10000];
+ int top = -1;
+ for (int i = 0; s[i]; i++) {
+ if (s[i] == '(' || s[i] == '{' || s[i] == '[') {
+ stack[++top] = s[i];
+ } else {
+ if (top == -1) return false;
+ char c = stack[top--];
+ if ((s[i] == ')' && c != '(') || 
+ (s[i] == '}' && c != '{') || 
+ (s[i] == ']' && c != '[')) {
+ return false;
+ }
+ }
+ }
+ return top == -1;
+}

sol/solution/0001-0100/0020/Solution.cpp

@@ -0,0 +1,21 @@
+class Solution {
+public:
+ bool isValid(string s) {
+ stack<char> stack;
+ for (char c : s) {
+ if (c == '(' || c == '{' || c == '[') {
+ stack.push(c);
+ } else {
+ if (stack.empty()) return false;
+ char top = stack.top();
+ stack.pop();
+ if ((c == ')' && top != '(') || 
+ (c == '}' && top != '{') || 
+ (c == ']' && top != '[')) {
+ return false;
+ }
+ }
+ }
+ return stack.empty();
+ }
+};

sol/solution/0001-0100/0020/Solution.cs

@@ -0,0 +1,19 @@
+public class Solution {
+ public bool IsValid(string s) {
+ Stack<char> stack = new Stack<char>();
+ foreach (char c in s) {
+ if (c == '(' || c == '{' || c == '[') {
+ stack.Push(c);
+ } else {
+ if (stack.Count == 0) return false;
+ char top = stack.Pop();
+ if ((c == ')' && top != '(') || 
+ (c == '}' && top != '{') || 
+ (c == ']' && top != '[')) {
+ return false;
+ }
+ }
+ }
+ return stack.Count == 0;
+ }
+}

sol/solution/0001-0100/0020/Solution.dart

@@ -0,0 +1,19 @@
+class Solution {
+ bool isValid(String s) {
+ List<String> stack = [];
+ for (var c in s.split('')) {
+ if (c == '(' || c == '{' || c == '[') {
+ stack.add(c);
+ } else {
+ if (stack.isEmpty) return false;
+ var top = stack.removeLast();
+ if ((c == ')' && top != '(') || 
+ (c == '}' && top != '{') || 
+ (c == ']' && top != '[')) {
+ return false;
+ }
+ }
+ }
+ return stack.isEmpty;
+ }
+}

sol/solution/0001-0100/0020/Solution.erl

@@ -0,0 +1,19 @@
+-spec is_valid(S :: unicode:unicode_binary()) -> boolean().
+is_valid(S) ->
+ Chars = unicode:characters_to_list(S),
+ Pairs = #{ $) => $(, $] => $[, $} => ${ },
+ check(Chars, [], Pairs).
+check([], [], _Pairs) ->
+ true;
+check([], _Stack, _Pairs) ->
+ false;
+check([C | Rest], Stack, Pairs) ->
+ case maps:get(C, Pairs, undefined) of
+ undefined ->
+ check(Rest, [C | Stack], Pairs);
+ Open ->
+ case Stack of
+ [Open | Tail] -> check(Rest, Tail, Pairs);
+ _ -> false
+ end
+ end.

sol/solution/0001-0100/0020/Solution.ex

@@ -0,0 +1,12 @@
+defmodule Solution do
+ @spec is_valid(s :: String.t) :: boolean
+ def is_valid(s), do: match_brackets(s, [])
+ defp match_brackets(<<?(, rest::binary>>, stack), do: match_brackets(rest, [?( | stack])
+ defp match_brackets(<<?[, rest::binary>>, stack), do: match_brackets(rest, [?[ | stack])
+ defp match_brackets(<<?{, rest::binary>>, stack), do: match_brackets(rest, [?{ | stack])
+ defp match_brackets(<<?), rest::binary>>, [?( | stack]), do: match_brackets(rest, stack)
+ defp match_brackets(<<?], rest::binary>>, [?[ | stack]), do: match_brackets(rest, stack)
+ defp match_brackets(<<?}, rest::binary>>, [?{ | stack]), do: match_brackets(rest, stack)
+ defp match_brackets("", []), do: true
+ defp match_brackets(_, _), do: false
+end

sol/solution/0001-0100/0020/Solution.go

@@ -0,0 +1,20 @@
+func isValid(s string) bool {
+ stack := []rune{}
+ for _, c := range s {
+ if c == '(' || c == '{' || c == '[' {
+ stack = append(stack, c)
+ } else {
+ if len(stack) == 0 {
+ return false
+ }
+ top := stack[len(stack)-1]
+ stack = stack[:len(stack)-1]
+ if (c == ')' && top != '(') || 
+ (c == '}' && top != '{') || 
+ (c == ']' && top != '[') {
+ return false
+ }
+ }
+ }
+ return len(stack) == 0
+}

sol/solution/0001-0100/0020/Solution.java

@@ -0,0 +1,19 @@
+class Solution {
+ public boolean isValid(String s) {
+ Stack<Character> stack = new Stack<>();
+ for (char c : s.toCharArray()) {
+ if (c == '(' || c == '{' || c == '[') {
+ stack.push(c);
+ } else {
+ if (stack.isEmpty()) return false;
+ char top = stack.pop();
+ if ((c == ')' && top != '(') || 
+ (c == '}' && top != '{') || 
+ (c == ']' && top != '[')) {
+ return false;
+ }
+ }
+ }
+ return stack.isEmpty();
+ }
+}

sol/solution/0001-0100/0020/Solution.js

@@ -0,0 +1,21 @@
+/**
+ * @param {string} s
+ * @return {boolean}
+ */
+var isValid = function(s) {
+ const stack = [];
+ for (const c of s) {
+ if (c === '(' || c === '{' || c === '[') {
+ stack.push(c);
+ } else {
+ if (stack.length === 0) return false;
+ const top = stack.pop();
+ if ((c === ')' && top !== '(') || 
+ (c === '}' && top !== '{') || 
+ (c === ']' && top !== '[')) {
+ return false;
+ }
+ }
+ }
+ return stack.length === 0;
+};