The given code is a function isValid that takes a string s as an input and checks whether the parentheses, brackets, and curly braces in the string are validly matched. The function returns a boolean value true if the string has validly matched parentheses, brackets, and curly braces, and false otherwise.

Here's a step-by-step explanation of the code:

We declare a stack of characters st to keep track of the opening parentheses, brackets, and curly braces in the string.

We iterate over the characters in the string s using a range-based for loop.

Inside the loop, we check whether the current character c is an opening parentheses, bracket, or curly brace. If it is, we push it onto the stack.

If the current character c is not an opening parentheses, bracket, or curly brace, we check whether the stack is empty. If it is, the string is invalid because there is no matching opening parentheses, bracket, or curly brace.

If the stack is not empty, we pop the top character top from the stack and compare it to the current character c. If the characters do not match, the string is invalid because the opening and closing parentheses, brackets, or curly braces do not match.

char top = st.top();

st.pop();

if ((c == ')' && top != '(') || (c == ']' && top != '[') || (c == '}' && top != '{')) {

return false;

}

Once we have iterated over all the characters in the string, we check whether the stack is empty. If it is not empty, the string is invalid because there are unmatched opening parentheses, brackets, or curly braces.

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