[알고리즘] 1244. 스위치 켜고 끄기

0. 문제

 

1244번: 스위치 켜고 끄기

 

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1. 문제 이해

 

 

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2. 제출

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {

    public static char[] switches;
    public static int swi, stu;

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine());

        swi = Integer.parseInt(st.nextToken());

        st = new StringTokenizer(br.readLine());
        switches = new char[swi];
        for(int i=0; i<swi; i++) {
            switches[i] = st.nextToken().charAt(0);
        }

        //student
        st = new StringTokenizer(br.readLine());
        stu = Integer.parseInt(st.nextToken());

        for(int i =0; i<stu; i++) {
            st = new StringTokenizer(br.readLine());
            String gender = st.nextToken();
            if(gender.equals("1")) 
                man(Integer.parseInt(st.nextToken()));
            else if(gender.equals("2")) 
                woman(Integer.parseInt(st.nextToken()));
        }

        //result
        int cnt = 0;
        for(char c : switches) {
            System.out.print(c+ " ");
            cnt++;
            if(cnt==20) {
                System.out.println();
                cnt=0;
            }
        }
    }
    public static void man (int idx) {
//        System.out.println("man : " + idx);
        for(int i=idx; i<=swi; i++) {
            if(i%idx==0)
                toggle(i-1);
        }
    }
    public static void woman (int idx) {
//        System.out.println("woman : " + idx);
        int start = idx, end = idx;
        for(int i=1; i<swi; i++) {
            int left = idx - i;
            int right = idx + i;
            if(left < 1 || right > swi) break;
            if(switches[left -1] != switches[right -1]) break;
            start=left; end=right;
        }
        for(int i=start; i<=end; i++) {
            toggle(i-1);
        }
    }
    public static void toggle (int idx) {
        if(switches[idx]=='1') {
            switches[idx] ='0';
        } else if(switches[idx]=='0') {
            switches[idx] ='1';
        }
//        System.out.println("toggle : " + (idx+1) + " -> " + switches[idx]);
    }

}

풀어서 통과는 했지만 아쉬운 부분이 보인다.

 

toggle(i-1);
...
public static void toggle (int idx) {
    if(switches[idx]=='1') {
        switches[idx] ='0';
    } else if(switches[idx]=='0') {
        switches[idx] ='1';
    }
}

이 부분을 다음과 같이 고칠 수 있다.

 

switches[i-1] = switches[i-1]  == 1 ? 0 : 1;

삼항연산자를 사용하면 더 간단하게 풀 수 있다.

 

//before
public static void man (int idx) {
    for(int i=idx; i<=swi; i++) {
        if(i%idx==0)
            toggle(i-1);
    }
}
//after
public static void man (int idx) {
    for(int i=1; i*idx<=swi; i++){
        switches[i*idx-1] = switches[i*idx-1]  == '1' ? '0' : '1';
    }
}

//before
public static void woman (int idx) {
    int start = idx, end = idx;
    for(int i=1; i<swi; i++) {
        int left = idx - i;
        int right = idx + i;
        if(left < 1 || right > swi) break;
        if(switches[left -1] != switches[right -1]) break;
        start=left; end=right;
    }
    for(int i=start; i<=end; i++) {
        toggle(i-1);
    }
}
//after
public static void woman(int idx){
    switches[idx-1] = switches[idx-1] == '1' ? '0' : '1';
    for(int start = idx-1, end=idx+1; start>=1 && **e**nd<=swi; start--, end++){
        if(switches[start-1] == switches[end-1]){
            switches[start-1] = switches[start-1] == '1' ? '0' : '1';
            switches[end-1] = switches[end-1] == '1' ? '0' : '1';
        }else break;
    } 
}

 

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3. 최종

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {

    public static char[] switches;
    public static int swi, stu;

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine());

        swi = Integer.parseInt(st.nextToken());

        st = new StringTokenizer(br.readLine());
        switches = new char[swi+1];
        for(int i=1; i<=swi; i++) {
            switches[i] = st.nextToken().charAt(0);
        }

        //student
        st = new StringTokenizer(br.readLine());
        stu = Integer.parseInt(st.nextToken());

        for(int i =0; i<stu; i++) {
            st = new StringTokenizer(br.readLine());
            String gender = st.nextToken();
            if(gender.equals("1")) 
                man(Integer.parseInt(st.nextToken()));
            else if(gender.equals("2")) 
                woman(Integer.parseInt(st.nextToken()));
        }

        //result
        int cnt = 0;
        for(int i=1; i<=swi; i++) {
            System.out.print(switches[i]+ " ");
            cnt++;
            if(cnt==20) {
                System.out.println();
                cnt=0;
            }
        }
    }
    public static void man (int idx) {
        for(int i=1; i*idx<=swi; i++){
            switches[i*idx] = switches[i*idx] == '1' ? '0' : '1';
        }
    }
    public static void woman(int idx){
        switches[idx] = switches[idx] == '1' ? '0' : '1';
        for(int start = idx-1, end=idx+1; start>0 && end<=swi; start--, end++){
            if(switches[start] == switches[end]){
                switches[start] = switches[start] == '1' ? '0' : '1';
                switches[end] = switches[end] == '1' ? '0' : '1';
            }else break;
        } 
    }
}

• switches = new char[swi+1]; : 계속 인덱스마다 -1 하기보다는 한 자리를 크게 쓰자.

 

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