#leetcode

ValidParenthesis.java

import java.util.Stack;
public class ValidParenthesis {
    public boolean isValid(String s) {
        if(s == null || s.length() == 0 || s.length() % 2 == 1) return false;
        
        Stack<Character> chars = new Stack<Character>();
        int len = s.length();
        for(int i = 0; i < len; i++){
            char c = s.charAt(i);
            if(!validCharacter(c)) return false;
            if(isLeftHalf(c)) chars.push(c);
            else{
                if(chars.size() == 0) return false;
                char top = chars.peek();
                if(!match(top, c)) return false;
                chars.pop();
            }
        }
        if(chars.size() != 0) return false;
        return true;
    }
    
    private boolean validCharacter(char c){
        switch(c){
            case '(':
            case ')':
            case '[':
            case ']':
            case '{':
            case '}':
                return true;
            default:
                return false;
        }
    }
    
    private boolean isLeftHalf(char c){
        switch(c){
            case '(':
            case '[':
            case '{':
                return true;
            default:
                return false;
        }
    }
    
    private boolean match(char left, char right){
        if(left == '(' && right == ')') return true;
        if(left == '[' && right == ']') return true;
        if(left == '{' && right == '}') return true;
        return false;
    }
}