Find whether the given expression is balanced

FindBrancketBalancing

import XCTest

let patterns: [String: String] = [
    "{": "}",
    "[": "]",
    "(": ")"
]

func isValid(with input: String) -> Bool! {
    let charArr = input.split(separator: " ")
    
    var holder = [String]()
    charArr.forEach { item in
        let holderPrev = holder.last

        if let holderPrev = holderPrev {
            if patterns[holderPrev] ?? "" == item {
                holder.popLast()
            } else {
                holder.append(String(item))
            }
        } else {
            holder.append(String(item))
        }
    }
    
    return holder.isEmpty
}

let input1 = "{ [ ( ) ] }"
XCTAssertTrue(isValid(with: input1)!)

let input2 = "{ [ } ]"
XCTAssertFalse(isValid(with: input2)!)

let input3 = "{ { [ ]"
XCTAssertFalse(isValid(with: input3)!)

let input4 = "{ [ ( ( ( ) ) ) ] } { }"
XCTAssertTrue(isValid(with: input4)!)