feat: solve No.2140

Author: BaffinLee

Diff for: 2101-2200/2140. Solving Questions With Brainpower.md

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+# 2140. Solving Questions With Brainpower
+
+- Difficulty: Medium.
+- Related Topics: Array, Dynamic Programming.
+- Similar Questions: House Robber, Frog Jump.
+
+## Problem
+
+You are given a **0-indexed** 2D integer array `questions` where `questions[i] = [pointsi, brainpoweri]`.
+
+The array describes the questions of an exam, where you have to process the questions **in order** (i.e., starting from question `0`) and make a decision whether to **solve** or **skip** each question. Solving question `i` will **earn** you `pointsi` points but you will be **unable** to solve each of the next `brainpoweri` questions. If you skip question `i`, you get to make the decision on the next question.
+
+
+	For example, given `questions = [[3, 2], [4, 3], [4, 4], [2, 5]]`:
+
+	
+		
+- If question `0` is solved, you will earn `3` points but you will be unable to solve questions `1` and `2`.
+		
+- If instead, question `0` is skipped and question `1` is solved, you will earn `4` points but you will be unable to solve questions `2` and `3`.
+	
+	
+
+
+Return **the **maximum** points you can earn for the exam**.
+
+ 
+Example 1:
+
+```
+Input: questions = [[3,2],[4,3],[4,4],[2,5]]
+Output: 5
+Explanation: The maximum points can be earned by solving questions 0 and 3.
+- Solve question 0: Earn 3 points, will be unable to solve the next 2 questions
+- Unable to solve questions 1 and 2
+- Solve question 3: Earn 2 points
+Total points earned: 3 + 2 = 5. There is no other way to earn 5 or more points.
+```
+
+Example 2:
+
+```
+Input: questions = [[1,1],[2,2],[3,3],[4,4],[5,5]]
+Output: 7
+Explanation: The maximum points can be earned by solving questions 1 and 4.
+- Skip question 0
+- Solve question 1: Earn 2 points, will be unable to solve the next 2 questions
+- Unable to solve questions 2 and 3
+- Solve question 4: Earn 5 points
+Total points earned: 2 + 5 = 7. There is no other way to earn 7 or more points.
+```
+
+ 
+**Constraints:**
+
+
+	
+- `1 <= questions.length <= 105`
+	
+- `questions[i].length == 2`
+	
+- `1 <= pointsi, brainpoweri <= 105`
+
+
+
+## Solution
+
+```javascript
+/**
+ * @param {number[][]} questions
+ * @return {number}
+ */
+var mostPoints = function(questions) {
+    var dp = Array(questions.length);
+    for (var i = questions.length - 1; i >= 0; i--) {
+        var [points, brainpower] = questions[i];
+        dp[i] = Math.max(
+            points + (dp[i + brainpower + 1] || 0),
+            dp[i + 1] || 0,
+        );
+    }
+    return dp[0];
+};
+```
+
+**Explain:**
+
+Dynamic-programming.
+
+**Complexity:**
+
+* Time complexity : O(n).
+* Space complexity : O(n).