LeetCode - Valid Parentheses
Problem description
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:
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Input: "()"
Output: true
Example 2:
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Input: "()[]{}"
Output: true
Example 3:
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Input: "(]"
Output: false
Example 4:
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Input: "([)]"
Output: false
Example 5:
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Input: "{[]}"
Output: true
Analysis
This is a easy question and use stack is the easiest way to solve it.
Here’s the code:
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public class ValidParentheses {
public boolean isValid(String s) {
List<Character> stack = new ArrayList<>();
for (char c : s.toCharArray()) {
if (c == ')') {
if (stack.isEmpty() || stack.remove(stack.size() - 1) != '(') {
return false;
}
} else if (c == ']') {
if (stack.isEmpty() || stack.remove(stack.size() - 1) != '[') {
return false;
}
} else if (c == '}') {
if (stack.isEmpty() || stack.remove(stack.size() - 1) != '{') {
return false;
}
} else {
stack.add(c);
}
}
return stack.size() == 0;
}
}
What to improve
- must be careful about the index out of bound exception, should check index range before every operation of array.