are braces balanced

t11e19.validbraces.cpp

// t11e19.validbraces.cpp
// juanfc 2023-11-22
// 

#include <iostream>
using namespace std;

const string OPENING = "([{<“‘";
const string CLOSING = ")]}>”’";

void test(string s);

int main()
{
    test( "(){}[]" );
    test( "(}"     );
    test( "[(])"   );
    test( "([{}])" );
    return 0;
}

bool validBraces(string s);
void test(string s)
{
    if (validBraces(s))
        cout << '"' << s << "\": has braces balanced" << endl;
    else
        cout << '"' << s << "\": has NOT braces balanced" << endl;
}

int find(string s, char c);
bool validBraces(string s)
{
    string stack;
    int i = 0;
    bool balanced = true;
    while (i < s.length() and balanced) {
        int posPair = find(OPENING, s[i]);
        if (posPair >= 0)
            stack += OPENING[posPair];
        else {
            posPair = find(CLOSING, s[i]);
            if (posPair >= 0) {
                // is the last opening the partner or this closing?
                int prev = find(OPENING, stack[stack.length()-1]);
                balanced = prev == posPair;
                if (balanced)
                    stack = stack.substr(0, stack.length()-1);
            }
        }
        ++i;
    }
    return stack == "";
}

int find(string s, char c)
{
    int i = 0;
    while (i < s.length() and s[i] != c)
        ++i;
    return (i < s.length())? i: -1;
}