LeetCode : Valid Parentheses

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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.

class Solution {public:    bool isValid(string s) {        stack<char>brack;        int i = 0;        while(i<s.size())        {            char c = s[i];            if(c=='('||c=='['||c=='{')                   brack.push(c);            else            {                if(brack.size()==0)                    return false;                char pre = brack.top();                switch(c)                {                    case ')':                       if(pre=='(')                          brack.pop();                       else                          return false;                       break;                    case ']':                       if(pre=='[')                          brack.pop();                       else                          return false;                          break;                    case '}':                       if(pre=='{')                          brack.pop();                       else                          return false;                          break;                }            }            ++i;        }        if(brack.size()==0)            return true;        else            return false;    }};

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