18258 java solution

solution/data_structure/18258/Main.java

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+// Authored by : semInDev
+// Co-authored by : -
+// Link : https://www.acmicpc.net/problem/18258
+
+import java.util.*;
+import java.io.*;
+
+public class Main {
+
+	public static void main(String[] args) throws IOException {
+        FastReader input = new FastReader();
+
+        Deque<Integer> deque = new ArrayDeque<>(); // back명령어를 사용하기 위해 deque이용
+        StringBuilder sb = new StringBuilder();
+
+        int N = input.nextInt();
+		while(N-->0) {
+			String cmd = input.next();			
+			switch (cmd) {
+				case "push":
+					int X = input.nextInt();
+					deque.add(X);
+					break;
+				case "pop":
+					if(deque.isEmpty()) sb.append(-1+"\n");
+					else sb.append(deque.poll()+"\n");
+					break;
+				case "size":
+					sb.append(deque.size()+"\n");
+					break;
+				case "empty":
+					if(deque.isEmpty()) sb.append(1+"\n");
+					else sb.append(0+"\n");
+					break;
+				case "front":
+					if(deque.isEmpty()) sb.append(-1+"\n");
+					else sb.append(deque.peekFirst()+"\n");
+					break;
+				case "back":
+					if(deque.isEmpty()) sb.append(-1+"\n");
+					else sb.append(deque.peekLast()+"\n");
+			}
+		}
+        System.out.print(sb);
+	}
+
+    static class FastReader {
+        BufferedReader br;
+        StringTokenizer st;
+
+        public FastReader() throws IOException{
+        	br = new BufferedReader(new InputStreamReader(System.in)); //백준 제출 시 주석해제를 하면 됩니다.
+        	// br = new BufferedReader(new FileReader("input.txt")); //IDE 실행 시 주석해제를 하면 됩니다.
+        }
+
+        String next() {
+            while(st == null || !st.hasMoreElements()) {
+                try {
+                    st = new StringTokenizer(br.readLine());
+                }
+                catch (IOException e) {
+                    e.printStackTrace();
+                }
+            }
+            return st.nextToken();
+        }
+
+        int nextInt() { return Integer.parseInt(next()); }
+        long nextLong() { return Long.parseLong(next()); }
+        String nextLine() {
+            String str = "";
+            try {
+                str = br.readLine();
+            }
+            catch (IOException e) {
+                e.printStackTrace();
+            }
+            return str;
+        }
+    }
+}