Algorithm, boj, 2579(계단오르기), dp

 package org.baekjoon;
 import java.util.Scanner;
 public class test2579 {
 	public static void main(String[] args) {
 		// TODO Auto-generated method stub
 		Scanner sc = new Scanner(System.in);
 		int stair[] = new int[300+1];
 		int n = sc.nextInt();
 		for (int i=1; i<=n; i++) {
 			stair[i] = sc.nextInt();
 		}
 		int sum[] = new int[stair.length];
 		for (int i = 1; i <= 3; i++) {
 		 if (i != 3) { //세번째까지 도달하지 않았을 경우 1번째 계단 + 2번째 계단
 		 sum[i] = sum[i-1] + stair[i];
 		 }
 		 else {
 		 	sum[i] = Math.max(sum[i-2] + stair[i], stair[i] + stair[i-1] );
 		 }
 		}
 		for (int i = 4; i <= n; i++) {
 			sum[i] = Math.max(sum[i-3] + stair[i-1] + stair[i], sum[i-2] + stair[i]);
 		}
 		System.out.print(sum[n]);
 	}
 }