백준 9095: 1, 2, 3 더하기

import java.util.*;
import java.lang.*;
import java.io.*;

class Main {
    public static void main(String[] args) throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int N = Integer.parseInt(br.readLine());

        for(int i=0; i<N; i++){
            int num = Integer.parseInt(br.readLine());

            int[] dp = new int[num+1];
            dp[1]=1;
            if(num>=2) dp[2]=2;
            if(num>=3) dp[3]=4;
            for(int k=4; k<=num; k++){
                dp[k]=dp[k-1]+dp[k-2]+dp[k-3];
            }
            System.out.println(dp[num]);
        }
    }
}

// ✘ 비효율
for(int i=0; i<N; i++){
    int num = Integer.parseInt(br.readLine());
    int[] dp = new int[num+1];  // 매번 새로 생성
    // ...
}

if(num>=2) dp[2]=2;
if(num>=3) dp[3]=4;

import java.io.*;

class Main {
    public static void main(String[] args) throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int T = Integer.parseInt(br.readLine());
        
        // 최댓값 11까지 미리 계산
        int[] dp = new int[12];
        dp[1] = 1;
        dp[2] = 2;
        dp[3] = 4;
        
        for(int i=4; i<=11; i++){
            dp[i] = dp[i-1] + dp[i-2] + dp[i-3];
        }
        
        StringBuilder sb = new StringBuilder();
        for(int i=0; i<T; i++){
            int n = Integer.parseInt(br.readLine());
            sb.append(dp[n]).append('\n');
        }
        
        System.out.print(sb);
    }
}