Valid Parentheses
Given a string containing just the characters '('
, ')'
, '{'
, '}'
, '['
and ']'
, determine if the input string is valid.
The brackets must close in the correct order, "()"
and "()[]{}"
are all valid but "(]"
and "([)]"
are not.
分析:字符串符号配对。采用栈的后进先出特点就可解决。
利用一个栈来保存前括号,然后有后括号来时弹出栈顶来判断。
public class Solution { public boolean isValid(String s) { Stack<Character> st = new Stack<Character>(); for(int i=0; i<s.length(); i++) { char temp = s.charAt(i); if(temp == '[' || temp == '{' || temp == '(') { st.add(temp); } else { if(st.empty()) { return false; } char c = st.peek(); if((temp == ']' && c == '[') || (temp == '}' && c == '{') || (temp == ')' && c == '(')) { st.pop(); }else { return false; } } } return st.empty(); }