day4: (1) dp/9095

dp/더하기_1_2_3.java

@@ -0,0 +1,111 @@
+package test.boj.dp;
+
+import org.junit.*;
+
+import java.io.*;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Stack;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class 더하기_1_2_3 {
+
+    public static void main(String[] args) throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+
+        int num = Integer.parseInt(br.readLine());
+
+        for(int t_case = 0 ; t_case < num ; t_case++){
+
+            int n = Integer.parseInt(br.readLine());
+            int dp[] = new int[12];
+
+            dp[1] = 1;
+            dp[2] = 2;
+            dp[3] = 4;
+
+            for(int i = 4; i <= n ; i++){
+                dp[i] = dp[i-1] + dp[i-2] + dp[i-3];
+            }
+
+            bw.append(String.valueOf(dp[n]+"\n"));
+        }
+        bw.close();
+    }
+
+//    public static void main(String[] args) {
+//        Scanner sc = new Scanner(System.in);
+//        int n = sc.nextInt();
+//        int[] result = solution(IntStream.range(0, n)
+//                .map(i -> sc.nextInt())
+//                .toArray());
+//
+//        System.out.println(Arrays.stream(result).mapToObj(String::valueOf).collect(Collectors.joining("\n")));
+//    }
+
+    @Test
+    public void test_점화식_사용() {
+        assertThat(solution2(new int[]{1, 2, 3}))
+                .isEqualTo(new int[]{1, 2, 4});
+
+        assertThat(solution2(new int[]{4, 7, 10}))
+                .isEqualTo(new int[]{7, 44, 274});
+    }
+
+    private int[] solution2(int[] nums) {
+        int[] result = new int[nums.length];
+        int dp[] = new int[12];
+        dp[1] = 1;
+        dp[2] = 2;
+        dp[3] = 4;
+
+        for(int i = 4; i <= 10; i++){
+            dp[i] = dp[i-1] + dp[i-2] + dp[i-3];
+        }
+
+        for(int tCase = 0; tCase < nums.length; tCase++){
+            int caseNum = nums[tCase];
+            result[tCase] = dp[caseNum];
+        }
+        return result;
+    }
+
+    @Test
+    public void test_단계마다_계산() {
+        assertThat(solution(new int[]{1, 2, 3}))
+                .isEqualTo(new int[]{1, 2, 4});
+
+        assertThat(solution(new int[]{4, 7, 10}))
+            .isEqualTo(new int[]{7, 44, 274});
+    }
+
+    private static int[] solution(int[] testCases) {
+        final int[] result = new int[testCases.length];
+        Stack<List<Integer>> stack = new Stack<>();
+        stack.push(Arrays.asList(1, 2, 3));
+
+        for (int step = 0; step < 10; step++) {
+            List<Integer> prevSums = stack.pop();
+            List<Integer> sums = new ArrayList<>();
+            for (int prevSum : prevSums) {
+                for (int j = 0; j < testCases.length; j++) {
+                    if (prevSum == testCases[j]) {
+                        result[j]++;
+                    }
+                }
+
+                if (step == 9) break;
+
+                for (int numToSum = 1; numToSum <= 3; numToSum++) {
+                    int sum = numToSum + prevSum;
+                    sums.add(sum);
+                }
+            }
+            stack.push(sums);
+        }
+        return result;
+    }
+}