[leetcode]Valid Parentheses

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.

 

算法思路：

很经典的栈问题，我采用了大量的数据结构，以保证

代码如下：

public class Solution {
    public boolean isValid(String s) {
        if(s == null || (s.length() & 1 )== 1) return false;
        Set<Character> leftSet = new HashSet<Character>();
        Set<Character> rightSet = new HashSet<Character>();
        char[] left = {'(','[','{'};
        char[] right = {')',']','}'};
        Map<Character,Character> pair = new HashMap<Character,Character>();
        for(int i = 0; i < left.length;leftSet.add(left[i]),pair.put(left[i], right[i++]));
        for(int i = 0; i < right.length;rightSet.add(right[i++]));
        Stack<Character> stack = new Stack<Character>();
        for(int i = 0; i < s.length(); i++){
            char c = s.charAt(i);
            if(leftSet.contains(c)) {
                stack.push(c);
            }else if(rightSet.contains(c)){
                if(stack.isEmpty() || c != pair.get(stack.pop()) ) return false; 
            }
        }
         return stack.isEmpty();
    }
}

其实完全木有必要，但是我学的数据结构还是多用比较好