[20250826] BOJ / G5 / 1, 2, 3 더하기 4 / 이인희

Author: LiiNi-coder

LiiNi-coder/202508/26 BOJ 1, 2, 3 더하기 4.md

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+```java
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+
+public class Main {
+	private static BufferedReader br;
+	private static int t;
+	private static int n;
+	private static int[][] dp;
+
+	public static void main(String[] args) throws IOException {
+		br = new BufferedReader(new InputStreamReader(System.in));
+		t = Integer.parseInt(br.readLine());
+		int maxN = 10000;
+		dp = new int[4][maxN + 1];
+		dp[1][1] = 1; //1
+		dp[1][2] = 1; //1+1
+		dp[2][2] = 1; //2
+		dp[1][3] = 1; //1+1+1
+		dp[2][3] = 1; //2+1
+		dp[3][3] = 1; //3
+
+		for (int i = 1; i <= 3; i++) {
+			for (int j = 1; j <= maxN; j++) {
+				dp[0][j] += dp[i][j];
+			}
+		}
+
+		for (int i = 4; i <= maxN; i++) {
+			//맨 앞 항이 1 -> 1 + (나머지를 1,2,3으로 만듦)
+			dp[1][i] = dp[0][i - 1];
+
+			// 맨 앞 항이 2 -> 2 + (나머지를 2,3으로 만듦)
+			dp[2][i] = dp[2][i - 2] + dp[3][i - 2];
+			if (i == 2) dp[2][i] = 1;
+
+			// 맨 앞 항이 3 -> 3 + (나머지를 3으로 만듦)
+			dp[3][i] = dp[3][i - 3];
+			if (i == 3) dp[3][i] = 1;
+
+			dp[0][i] = dp[1][i] + dp[2][i] + dp[3][i];
+		}
+
+		StringBuilder sb = new StringBuilder();
+		for(int tt = 0; tt<t; tt++) {
+			n = Integer.parseInt(br.readLine());
+			sb.append(dp[0][n]).append("\n");
+		}
+		System.out.print(sb);
+        
+        br.close();
+	}
+}
+```