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ValidParen.java
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82 lines (55 loc) · 1.67 KB
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import java.util.*;
public class ValidParen {
public static 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;
}
// Pop the last char from stack
char top = stack.pop();
// check it matches the current closing
if ((c == ')' && top != '(') ||
(c == '}' && top != '{') ||
(c == ']' && top != '[')) {
return false;
}
}
}
return stack.isEmpty();
}
public static void main(String[] args) {
String s = "()";
System.out.println(isValid(s));
}
}
/*
https://leetcode.com/problems/valid-parentheses/
1. Use a stack
push each opening bracket onto the stack
for a closing brack, check if it matches a top elem of stack
if so, pop the top elem
if not or stack is empty, string invalid
after processing; the stack needs to be empty
Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
An input string is valid if:
Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.
Every close bracket has a corresponding open bracket of the same type.
Example 1:
Input: s = "()"
Output: true
Example 2:
Input: s = "()[]{}"
Output: true
Example 3:
Input: s = "(]"
Output: false
Example 4:
Input: s = "([])"
Output: true
*/