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def isValid(s: str) -> bool:
Initializes the function `isValid` which takes a string `s` containing brackets and returns a boolean indicating if the string is valid.
    stack = []
Creates an empty list to use as our stack data structure for tracking opening brackets.
    mapping = {')': '(', '}': '{', ']': '['}
Creates a dictionary mapping each closing bracket to its corresponding opening bracket for easy matching.
    for char in s:
Loops through each character in the input string one by one.
        if char in mapping:
Checks if the current character is a closing bracket (exists as a key in mapping).
            if not stack or stack.pop() != mapping[char]:
If stack is empty OR the popped opening bracket doesn't match this closing bracket, the string is invalid.
                return False
Return False immediately if we find a mismatch or extra closing bracket.
        else:
If the character is not a closing bracket, it must be an opening bracket.
            stack.append(char)
Push the opening bracket onto the stack to be matched later with its closing bracket.
    return len(stack) == 0
Return True only if stack is empty (all opening brackets were matched).

public boolean isValid(String s) {
Initializes the function `isValid` which takes a string `s` and returns a boolean indicating validity.
    Deque<Character> stack = new ArrayDeque<>();
Creates a Deque (double-ended queue) to use as a stack for tracking opening brackets.
    for (char c : s.toCharArray()) {
Loops through each character in the input string after converting it to a char array.
        if (c == '(') {
Checks if the current character is an opening parenthesis.
            stack.push(')');
Push the corresponding closing bracket onto the stack (clever matching trick!).
        } else if (c == '{') {
Checks if the current character is an opening curly brace.
            stack.push('}');
Push the corresponding closing curly brace onto the stack.
        } else if (c == '[') {
Checks if the current character is an opening square bracket.
            stack.push(']');
Push the corresponding closing square bracket onto the stack.
        } else if (stack.isEmpty() || stack.pop() != c) {
If it's a closing bracket: if stack is empty OR popped element doesn't match, string is invalid.
            return false;
Return False immediately if we find a mismatch or extra closing bracket.
        }
End of the if-else chain.
    }
End of the for loop.
    return stack.isEmpty();
Return True only if stack is empty (all opening brackets were matched).
}
End of the function.

bool isValid(string s) {
Initializes the function `isValid` which takes a string `s` and returns a boolean indicating validity.
    stack<char> st;
Creates a stack of characters to track opening brackets.
    for (char c : s) {
Range-based for loop to iterate through each character in the string.
        if (c == '(' || c == '{' || c == '[') {
Checks if the current character is any type of opening bracket.
            st.push(c);
Push the opening bracket onto the stack for later matching.
        } else {
If it's not an opening bracket, it must be a closing bracket.
            if (st.empty()) return false;
If stack is empty when we encounter a closing bracket, there's no matching opener — invalid!
            char top = st.top(); st.pop();
Get the top element from stack and remove it (we need to check if it matches).
            if ((c == ')' && top != '(') ||
Check if closing parenthesis doesn't match opening parenthesis.
                (c == '}' && top != '{') ||
Check if closing curly brace doesn't match opening curly brace.
                (c == ']' && top != '[')) {
Check if closing square bracket doesn't match opening square bracket.
                return false;
If any bracket type doesn't match, return False immediately.
            }
End of the mismatch check if statement.
        }
End of the if-else block.
    }
End of the for loop.
    return st.empty();
Return True only if stack is empty (all brackets were properly matched).
}
End of the function.