Add solution #1997

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,677 LeetCode solutions in JavaScript
+# 1,678 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1532,6 +1532,7 @@
 1994|[The Number of Good Subsets](./solutions/1994-the-number-of-good-subsets.js)|Hard|
 1995|[Count Special Quadruplets](./solutions/1995-count-special-quadruplets.js)|Easy|
 1996|[The Number of Weak Characters in the Game](./solutions/1996-the-number-of-weak-characters-in-the-game.js)|Medium|
+1997|[First Day Where You Have Been in All the Rooms](./solutions/1997-first-day-where-you-have-been-in-all-the-rooms.js)|Medium|
 2000|[Reverse Prefix of Word](./solutions/2000-reverse-prefix-of-word.js)|Easy|
 2011|[Final Value of Variable After Performing Operations](./solutions/2011-final-value-of-variable-after-performing-operations.js)|Easy|
 2016|[Maximum Difference Between Increasing Elements](./solutions/2016-maximum-difference-between-increasing-elements.js)|Easy|

solutions/1997-first-day-where-you-have-been-in-all-the-rooms.js

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+/**
+ * 1997. First Day Where You Have Been in All the Rooms
+ * https://leetcode.com/problems/first-day-where-you-have-been-in-all-the-rooms/
+ * Difficulty: Medium
+ *
+ * There are n rooms you need to visit, labeled from 0 to n - 1. Each day is labeled, starting
+ * from 0. You will go in and visit one room a day.
+ *
+ * Initially on day 0, you visit room 0. The order you visit the rooms for the coming days is
+ * determined by the following rules and a given 0-indexed array nextVisit of length n:
+ * - Assuming that on a day, you visit room i,
+ * - if you have been in room i an odd number of times (including the current visit), on the next
+ *   day you will visit a room with a lower or equal room number specified by nextVisit[i]
+ *   where 0 <= nextVisit[i] <= i;
+ * - if you have been in room i an even number of times (including the current visit), on the
+ *   next day you will visit room (i + 1) mod n.
+ *
+ * Return the label of the first day where you have been in all the rooms. It can be shown
+ * that such a day exists. Since the answer may be very large, return it modulo 109 + 7.
+ */
+
+/**
+ * @param {number[]} nextVisit
+ * @return {number}
+ */
+var firstDayBeenInAllRooms = function(nextVisit) {
+  const MOD = 1e9 + 7;
+  const n = nextVisit.length;
+  const dp = new Array(n).fill(0);
+
+  for (let i = 1; i < n; i++) {
+    dp[i] = (2 * dp[i - 1] + 2 - dp[nextVisit[i - 1]] + MOD) % MOD;
+  }
+
+  return dp[n - 1];
+};