This approach uses a stack to efficiently match opening and closing brackets. The stack stores opening brackets, and for each closing bracket encountered, it checks if it closes the last opened bracket (top of the stack).
Time Complexity: O(n), where n is the length of the string, since we process each character once.
Space Complexity: O(n) in the worst case if the string consists only of opening brackets.
1import java.util.Stack;
2
3public class Solution {
4 public boolean isValid(String s) {
5 Stack<Character> stack = new Stack<>();
6 for (char c : s.toCharArray()) {
7 if (c == '(' || c == '{' || c == '[') {
8 stack.push(c);
9 } else {
10 if (stack.isEmpty()) return false;
11 char top = stack.pop();
12 if ((c == ')' && top != '(') ||
13 (c == '}' && top != '{') ||
14 (c == ']' && top != '['))
15 return false;
16 }
17 }
18 return stack.isEmpty();
19 }
20}The Java solution employs a stack to process and match each bracket in the string. If there's any imbalance or mismatched pair, it returns false.
This approach uses two pointers with stack-like behavior internally, taking advantage of simple list operations for push and pop.
Time Complexity: O(n)
Space Complexity: O(n/2) = O(n)
1using System;
2using System.Collections.Generic;
3
4public class Solution {
5 public bool IsValid(string s) {
6 if (s.Length % 2 != 0) return false;
7
8 var stack = new List<char>();
9 foreach (char c in s) {
10 if (c == '(' || c == '{' || c == '[') {
11 stack.Add(c);
12 } else {
13 if (stack.Count == 0) return false;
14 char top = stack[stack.Count - 1];
15 stack.RemoveAt(stack.Count - 1);
16 if ((c == ')' && top != '(') ||
17 (c == '}' && top != '{') ||
18 (c == ']' && top != '['))
19 return false;
20 }
21 }
22 return stack.Count == 0;
23 }
24}
25
26public class Program {
27 public static void Main() {
28 var solution = new Solution();
29 Console.WriteLine(solution.IsValid("()[]{}")); // Output: True
30 Console.WriteLine(solution.IsValid("(]")); // Output: False
31 }
32}The C# solution capitalizes on List operations like Add and RemoveAt, imitating stack-like behavior without the conventional stack class, enabling fluid manipulation on a character basis.