leetcode 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.

括号匹配问题

利用堆栈匹配

bool isValid(char* s) {
//构造一个堆栈，存放s
int len=strlen(s);

if(len==0)
return true;

char * stack=(char *)malloc(sizeof(char)*len);
int top=0;

int i;
for(i=0;i<len;i++)
{
if(top==0)
{
stack[top]=s[i];
top++;
}
else//top>0时
{
if( (stack[top-1] == '(' && s[i]==')') || (stack[top-1]=='[' && s[i]==']') || (stack[top-1]=='{' && s[i]=='}') )
{
top--;
}
else
{
stack[top]=s[i];
top++;
}
}

}

if(top==0)
return true;
else
return false;

}