isBalanced

// Complete the isBalanced function below.
func isBalanced(s: String) -> String {
    let openBrackets = "{([".replacingOccurrences(of: "", with: "")
    let closeBrackets = "})]"
    let brackets = ["]": "[", ")": "(", "}": "{"]
    
    guard s.count > 1 else {
        return "NO"
    }
    guard !closeBrackets.contains(s.first!) else { return "NO" }
    
    var stack: [Character] = []
    
    for char in s {
        if openBrackets.contains(char) {
            stack.append(char)
        } else if closeBrackets.contains(char) {
            if stack.isEmpty || String(stack.popLast()!) != brackets[String(char)]! {
                return "NO"
            }
        }
    }
    return stack.isEmpty ? "YES" : "NO"
}