【Valid Parentheses】cpp
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.
代码:
class Solution {
public:
bool isValid(string s) {
std::stack<char> result;
for ( size_t i = ; i < s.length(); ++i )
{
if ( s[i]=='(' || s[i]=='[' || s[i]=='{' )
{
result.push(s[i]);
continue;
}
if ( result.empty() ) return false;
char top = result.top();
if ( s[i]==')' && top!='(' ) return false;
if ( s[i]==']' && top!='[' ) return false;
if ( s[i]=='}' && top!='{') return false;
result.pop();
}
return result.empty();
}
};
tips:
口诀:左号进栈,右号出栈;出栈判断是否正确。
===========================================
第二次过这道题,凭感觉写了一份代码,稍微冗长一些;修改了一次AC了。
class Solution {
public:
bool isValid(string s) {
stack<char> sta;
int i = ;
while ( i<s.size() )
{
if ( s[i]=='(' || s[i]=='[' || s[i]=='{' )
{
sta.push(s[i]);
}
else if ( s[i]==')' || s[i]==']' || s[i]=='}' )
{
if ( sta.empty() ) return false;
if ( s[i]==')' )
{
if ( sta.top()=='(' )
{
sta.pop();
}
else
{
return false;
}
}
else if ( s[i]==']' )
{
if ( sta.top()=='[' )
{
sta.pop();
}
else
{
return false;
}
}
else
{
if ( sta.top()=='{' )
{
sta.pop();
}
else
{
return false;
}
}
}
else
{
return false;
}
++i;
}
return sta.empty();
}
};
有个地方不要遗漏:如果是右号,要判断一下stack是否为空。
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