LargestSqaure.swift

func largestSquare(_ s: String, width: Int) -> Int {
    
    let bits = s.map { $0 == "1" }
    let height = bits.count/width
    
    let longestLen = (0..<bits.count).reduce(0) { (curLongestLen, i) in
        let maxLen = min(width - i%width, height - i/width)
        let firstLenWhereAllBitsNotSet = (1...maxLen).first(where: { len in
            !(0..<len).allSatisfy { n in
                bits[i + width*(len-1) + n] && bits[i + (len-1) + width*n]
            }
        })
        let lastLenWhereAllBitsSet = (firstLenWhereAllBitsNotSet ?? maxLen+1) - 1
        return max(curLongestLen, lastLenWhereAllBitsSet)
    }
    
    return longestLen*longestLen
}