Add solution #2019

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,690 LeetCode solutions in JavaScript
+# 1,691 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1549,6 +1549,7 @@
 2016|[Maximum Difference Between Increasing Elements](./solutions/2016-maximum-difference-between-increasing-elements.js)|Easy|
 2017|[Grid Game](./solutions/2017-grid-game.js)|Medium|
 2018|[Check if Word Can Be Placed In Crossword](./solutions/2018-check-if-word-can-be-placed-in-crossword.js)|Medium|
+2019|[The Score of Students Solving Math Expression](./solutions/2019-the-score-of-students-solving-math-expression.js)|Hard|
 2027|[Minimum Moves to Convert String](./solutions/2027-minimum-moves-to-convert-string.js)|Easy|
 2033|[Minimum Operations to Make a Uni-Value Grid](./solutions/2033-minimum-operations-to-make-a-uni-value-grid.js)|Medium|
 2037|[Minimum Number of Moves to Seat Everyone](./solutions/2037-minimum-number-of-moves-to-seat-everyone.js)|Easy|

solutions/2019-the-score-of-students-solving-math-expression.js

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+/**
+ * 2019. The Score of Students Solving Math Expression
+ * https://leetcode.com/problems/the-score-of-students-solving-math-expression/
+ * Difficulty: Hard
+ *
+ * You are given a string s that contains digits 0-9, addition symbols '+', and multiplication
+ * symbols '*' only, representing a valid math expression of single digit numbers (e.g., 3+5*2).
+ * This expression was given to n elementary school students. The students were instructed to
+ * get the answer of the expression by following this order of operations:
+ * 1. Compute multiplication, reading from left to right; Then,
+ * 2. Compute addition, reading from left to right.
+ *
+ * You are given an integer array answers of length n, which are the submitted answers of the
+ * students in no particular order. You are asked to grade the answers, by following these rules:
+ * - If an answer equals the correct answer of the expression, this student will be rewarded
+ *   5 points;
+ * - Otherwise, if the answer could be interpreted as if the student applied the operators in
+ *   the wrong order but had correct arithmetic, this student will be rewarded 2 points;
+ * - Otherwise, this student will be rewarded 0 points.
+ *
+ * Return the sum of the points of the students.
+ */
+
+/**
+ * @param {string} s
+ * @param {number[]} answers
+ * @return {number}
+ */
+var scoreOfStudents = function(s, answers) {
+  const correct = eval(s.replace(/(\d)([*+])/g, '$1 $2 '));
+
+  const n = s.length;
+  const dp = new Map();
+
+  function compute(start, end) {
+    const key = `${start},${end}`;
+    if (dp.has(key)) return dp.get(key);
+
+    const results = new Set();
+    if (start === end) {
+      results.add(Number(s[start]));
+      dp.set(key, results);
+      return results;
+    }
+
+    for (let i = start + 1; i < end; i += 2) {
+      const leftResults = compute(start, i - 1);
+      const rightResults = compute(i + 1, end);
+      const op = s[i];
+
+      for (const left of leftResults) {
+        for (const right of rightResults) {
+          const val = op === '+' ? left + right : left * right;
+          if (val <= 1000) results.add(val);
+        }
+      }
+    }
+
+    dp.set(key, results);
+    return results;
+  }
+
+  const wrongAnswers = compute(0, n - 1);
+  let result = 0;
+
+  for (const answer of answers) {
+    if (answer === correct) result += 5;
+    else if (wrongAnswers.has(answer)) result += 2;
+  }
+
+  return result;
+};