2089번 '-2진수'

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;

import java.util.Stack;

class Main {

public static void main(String[] args) throws IOException {

BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

Stack<Integer> stack = new Stack<>();

int input = Integer.parseInt(in.readLine());

final int dividor = -2;

if(input == 0) {

System.out.println(0);

return;

}

while(input != 0) {

int quotient = input / dividor;

if(quotient * dividor < input) {

stack.push(1);

input = quotient;

} else if(quotient * dividor > input) {

quotient += 1;

stack.push(1);

input = quotient;

} else {

stack.push(0);

input = quotient;

}

}

while(!stack.isEmpty()) {

System.out.print(stack.pop());

}

System.out.println();

}

}

일단 종이를 준비하고, 주어진 수를 -2로 나누어가며 나머지가 0 또는 1만 나오게 적어본다.

그러면 풀 수 있다!

import Foundation

var input = Int(readLine()!)!

var stack = [Int]()

let dividor = -2

if input == 0 {

    print(0)

    exit(0)

}

while input != 0 {

   var quotient = input / dividor

    if quotient * dividor < input {

        stack.append(1)

    } else if quotient * dividor > input {

        quotient += 1

        stack.append(1)

    } else {

        stack.append(0)

    }

    input = quotient

}

while !stack.isEmpty {

    print(stack.popLast()!, terminator: "")

}

print()