Valid Parentheses Solutions in C++

// Source : https://oj.leetcode.com/problems/valid-parentheses/
// Author : Hao Chen
// Date   : 2014-06-30



#include <iostream>
#include <string>
#include <stack>
using namespace std;

bool isValid(string s) {
    stack<char> st;
    for(auto ch : s) {
        if (ch=='{' || ch =='[' || ch=='(' ) {
            st.push(ch);
        }else if (ch=='}' || ch ==']' || ch == ')' ){
            if (st.empty()) return false;
            char sch = st.top();
            if ( (sch=='{' && ch =='}') || (sch=='[' && ch==']') || (sch=='(' && ch==')' ) ){
                st.pop();
            }else {
                return false;
            }
        }else{
            return false;
        }
    }
    return st.empty();
}

int main(int argc, char**argv)
{
    string s = "{{}{[]()}}";
    if (argc>1){
        s = argv[1];
    }
    cout << "str = \"" << (s) << "\"" << endl;
    cout << isValid(s) << endl;
}

#include <string>
#include <stack>

using std::string; using std::stack; 

class Solution {
public:
    bool isValid(string s) {
        stack<char> stk;
        for (auto c : s)
            if (!stk.empty() && ((c == ')' && stk.top() == '(') || (c == '}' && stk.top() == '{') || (c == ']' && stk.top() == '['))) stk.pop();
            else stk.push(c);
        return stk.empty();
    }
};

/// Source : https://leetcode.com/problems/valid-parentheses/description/
/// Author : liuyubobobo
/// Time   : 2017-11-17

#include <iostream>
#include <stack>
#include <cassert>

using namespace std;

// Using Stack
// Time Complexity: O(n)
// Space Complexity: O(n)
class Solution {
public:
    bool isValid(string s) {

        stack<char> stack;
        for( int i = 0 ; i < s.size() ; i ++ )
            if( s[i] == '(' || s[i] == '{' || s[i] == '[')
                stack.push(s[i]);
            else{

                if( stack.size() == 0 )
                    return false;

                char c = stack.top();
                stack.pop();

                char match;
                if( s[i] == ')' )
                    match = '(';
                else if( s[i] == ']' )
                    match = '[';
                else{
                    assert( s[i] == '}' );
                    match = '{';
                }

                if(c != match)
                    return false;
            }

        if( stack.size() != 0 )
            return false;

        return true;
    }
};


void printBool(bool res){
    cout << (res ? "True" : "False") << endl;
}

int main() {

    printBool(Solution().isValid("()"));
    printBool(Solution().isValid("()[]{}"));
    printBool(Solution().isValid("(]"));
    printBool(Solution().isValid("([)]"));

    return 0;
}