C++实现LeetCode(20.验证括号)
时间：2022-02-25 10:15:23|栏目：C代码|点击： 次
[LeetCode] 20. Valid Parentheses 验证括号
Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
An input string is valid if:
- Open brackets must be closed by the same type of brackets.
- Open brackets must be closed in the correct order.
Note that an empty string is also considered valid.
Example 1:
Input: "()"
Output: true
Example 2:
Input: "()[]{}"
Output: true
Example 3:
Input: "(]"
Output: false
Example 4:
Input: "([)]"
Output: false
Example 5:
Input: "{[]}"
Output: true
这道题让我们验证输入的字符串是否为括号字符串，包括大括号，中括号和小括号。这里需要用一个栈，开始遍历输入字符串，如果当前字符为左半边括号时，则将其压入栈中，如果遇到右半边括号时，若此时栈为空，则直接返回 false，如不为空，则取出栈顶元素，若为对应的左半边括号，则继续循环，反之返回 false，代码如下：
方法一：
class Solution {
public:
bool isValid(string s) {
stack<char> parentheses;
for (int i = 0; i < s.size(); ++i) {
if (s[i] == '(' || s[i] == '[' || s[i] == '{') parentheses.push(s[i]);
else {
if (parentheses.empty()) return false;
if (s[i] == ')' && parentheses.top() != '(') return false;
if (s[i] == ']' && parentheses.top() != '[') return false;
if (s[i] == '}' && parentheses.top() != '{') return false;
parentheses.pop();
}
}
return parentheses.empty();
}
};
方法二：
class Solution {
public:
bool isValid(string s) {
int n = s.size();
if (n % 2 == 1) {
return false;
}
unordered_map<char, char> pairs = {
{')', '('},
{']', '['},
{'}', '{'}
};
stack<char> stk;
for (char ch: s) {
if (pairs.count(ch)) {
if (stk.empty() || stk.top() != pairs[ch]) {
return false;
}
stk.pop();
}
else {
stk.push(ch);
}
}
return stk.empty();
}
};
栏 目：C代码
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