[Stack] baekjoon-2867

Author: Seogeurim

Diff for: README.md

@@ -59,6 +59,7 @@
 | 02  |     | [Baekjoon-2504 괄호의 값](./src/Stack/P2504) |      |
 | 03  |     | [Baekjoon-3425 고스택](./src/Stack/P3425)    |      |
 | 04  |     | [Baekjoon-2493 탑](./src/Stack/P2493)        |      |
+| 05  | ⭐️ | [Baekjoon-2867 수열의 값](./src/Stack/P2867)        |      |
 
 ### Queue
 

Diff for: src/Stack/P2867/Main.java

@@ -0,0 +1,60 @@
+package Stack.P2867;
+
+import java.io.*;
+import java.util.Stack;
+
+public class Main {
+
+    static int N;
+    static int[] nums;
+
+    public static void main(String[] args) throws Exception {
+        System.setIn(new FileInputStream("src/Stack/P2867/input.txt"));
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+
+        N = Integer.parseInt(br.readLine());
+        nums = new int[N];
+        for (int i = 0; i < N; i++) nums[i] = Integer.parseInt(br.readLine());
+
+        Stack<Integer> stack = new Stack<>();
+
+        int[] LM = new int[N];
+        for (int i = 0; i < N; i++) {
+            while (!stack.empty() && (nums[stack.peek()] <= nums[i])) stack.pop();
+            LM[i] = stack.empty() ? 0 : stack.peek() + 1;
+            stack.push(i);
+        }
+
+        stack.clear();
+        int[] RM = new int[N];
+        for (int i = N-1; i >= 0; i--) {
+            while (!stack.empty() && (nums[stack.peek()] < nums[i])) stack.pop();
+            RM[i] = stack.empty() ? N-1 : stack.peek() - 1;
+            stack.push(i);
+        }
+
+        stack.clear();
+        int[] lm = new int[N];
+        for (int i = 0; i < N; i++) {
+            while (!stack.empty() && (nums[stack.peek()] >= nums[i])) stack.pop();
+            lm[i] = stack.empty() ? 0 : stack.peek() + 1;
+            stack.push(i);
+        }
+
+        stack.clear();
+        int[] rm = new int[N];
+        for (int i = N-1; i >= 0; i--) {
+            while (!stack.empty() && (nums[stack.peek()] > nums[i])) stack.pop();
+            rm[i] = stack.empty() ? N-1 : stack.peek() - 1;
+            stack.push(i);
+        }
+
+        long ans = 0;
+        for (int i = 0; i < N; i++) {
+            ans += nums[i] * (long)(i- LM[i] + 1) * (long)(RM[i] - i + 1);
+            ans -= nums[i] * (long)(i- lm[i] + 1) * (long)(rm[i] - i + 1);
+        }
+
+        System.out.println(ans);
+    }
+}

Diff for: src/Stack/P2867/README.md

@@ -0,0 +1,3 @@
+## [baekjoon-2867] 수열의 값
+
+![image](https://user-images.githubusercontent.com/22045163/93620960-cbe10380-fa15-11ea-8e01-6a4ad07d2633.png)

Diff for: src/Stack/P2867/input.txt

@@ -0,0 +1,5 @@
+4
+3
+1
+7
+2