Valid Parentheses
Given a string 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.
Note that an empty string is also considered valid.
Example 1:
Input: "()"
Output: true
Example 2:
Input: "()[]{}"
Output: true
Example 3:
Input: "(]"
Output: false
Example 4:
Input: "([)]"
Output: false
Example 5:
Input: "{[]}"
Output: true
Solution
Here is a solution using stack.
class Solution {
public boolean isValid(String s) {
Stack<Character> stack = new Stack<>();
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if (c == '(' || c == '{' || c == '[') {
stack.push(c);
} else {
if (stack.isEmpty()) {
return false;
}
char previous = stack.pop();
if (previous == '(') {
if (c != ')')
return false;
}
if (previous == '[') {
if (c != ']')
return false;
}
if (previous == '{') {
if (c != '}')
return false;
}
}
}
return stack.isEmpty();
}
}
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