20. Valid Parentheses
20. Valid Parentheses
题目
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.
解析
class Solution_20 {
public:
bool isValid(string s) {
if (s.size()<1)
{
return true;
}
stack<char> sta;
for (int i = 0; i < s.size();i++)
{
if (s[i]=='('||s[i]=='['||s[i]=='{')
{
sta.push(s[i]); //入栈
}else if ((s[i] == ')' || s[i] == ']' || s[i] == '}')&&sta.empty())
{
return false;
}
else if ((s[i] == ')'&&sta.top() == '(') || (s[i] == ']'&&sta.top() == '[') || (s[i] == '}'&&sta.top() == '{'))
{
sta.pop();
}else
{
return false;
}
}
if (sta.empty())
{
return true;
}
else
{
return false;
}
}
};
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