[LeetCode] 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.

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解題思路

借助棧來實現：

實現代碼

C++：

// Runtime: 0 ms
class Solution {
public:
    bool isValid(string s) {
        unordered_map mymap = {{'(', ')'}, {'[', ']'}, {'{', '}'}};
        stack mystack;
        for (int i = 0; i < s.length(); i++)
        {
            if (s[i] == '(' || s[i] == '[' || s[i] == '{')
            {
                mystack.push(s[i]);
            }
            else if (!mystack.empty() && (mymap[mystack.top()] == s[i]))
            {
                mystack.pop();
            }
            else
            {
                return false;
            }
        }

        return mystack.empty();
    }
};

Java:

// Runtime: 2 ms
public class Solution {
    public boolean isValid(String s) {
        Map map = new HashMap();
        Stack stack = new Stack();
        map.put('(', ')');
        map.put('[', ']');
        map.put('{', '}');
        for (int i = 0; i < s.length(); i++) {
            if (map.containsKey(s.charAt(i))) {
                stack.push(s.charAt(i));
            }
            else if (!stack.empty() && map.get(stack.peek()).equals(s.charAt(i))) {
                stack.pop();
            }
            else {
                return false;
            }
        }

        return stack.empty();
    }
}