LeetCode 20 -- 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.

---

主要思想还是盏。

public static boolean isValid(String s) {
    HashMap<Character, Character> map = new HashMap<Character, Character>();
    map.put('(', ')');
    map.put('[', ']');
    map.put('{', '}');
 
    Stack<Character> stack = new Stack<Character>();
 
    for (int i = 0; i < s.length(); i++) {
        char curr = s.charAt(i);
 
        if (map.keySet().contains(curr)) {
            stack.push(curr);
        } else if (map.values().contains(curr)) {
            if (!stack.empty() && map.get(stack.peek()) == curr) {
                stack.pop();
            } else {
                return false;
            }
        }
    }
 
    return stack.empty();
}

public class S20 {  
   
    public static void main(String[] args) {  
   
    }  
       
    // 用stack来检查  
    public boolean isValid(String s) {  
        Stack<Character> stack = new Stack<Character>();  
        for(int i=0; i<s.length(); i++){  
            char c = s.charAt(i);  
            // 如果遇到前括号就压入栈  
            if(c=='(' || c=='[' || c=='{'){  
                stack.push(c);  
            }else if(c==')' || c==']' || c=='}'){       // 遇到后括号就出栈  
                if(stack.size() == 0){  //  说明后括号太多了  
                    return false;  
                }  
                char cpop = stack.pop();  
                if(cpop=='(' && c==')'){  
                    continue;  
                }else if(cpop=='[' && c==']'){  
                    continue;  
                }else if(cpop=='{' && c=='}'){  
                    continue;  
                }  
                return false;  
            }  
        }  
        return stack.size()==0;  
    }  
   
}