Add solution #1269

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,203 LeetCode solutions in JavaScript
+# 1,204 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -964,6 +964,7 @@
 1263|[Minimum Moves to Move a Box to Their Target Location](./solutions/1263-minimum-moves-to-move-a-box-to-their-target-location.js)|Hard|
 1267|[Count Servers that Communicate](./solutions/1267-count-servers-that-communicate.js)|Medium|
 1268|[Search Suggestions System](./solutions/1268-search-suggestions-system.js)|Medium|
+1269|[Number of Ways to Stay in the Same Place After Some Steps](./solutions/1269-number-of-ways-to-stay-in-the-same-place-after-some-steps.js)|Hard|
 1287|[Element Appearing More Than 25% In Sorted Array](./solutions/1287-element-appearing-more-than-25-in-sorted-array.js)|Easy|
 1290|[Convert Binary Number in a Linked List to Integer](./solutions/1290-convert-binary-number-in-a-linked-list-to-integer.js)|Easy|
 1291|[Sequential Digits](./solutions/1291-sequential-digits.js)|Medium|

solutions/1269-number-of-ways-to-stay-in-the-same-place-after-some-steps.js

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+/**
+ * 1269. Number of Ways to Stay in the Same Place After Some Steps
+ * https://leetcode.com/problems/number-of-ways-to-stay-in-the-same-place-after-some-steps/
+ * Difficulty: Hard
+ *
+ * You have a pointer at index 0 in an array of size arrLen. At each step, you can move 1 position
+ * to the left, 1 position to the right in the array, or stay in the same place (The pointer should
+ * not be placed outside the array at any time).
+ *
+ * Given two integers steps and arrLen, return the number of ways such that your pointer is still
+ * at index 0 after exactly steps steps. Since the answer may be too large, return it modulo
+ * 109 + 7.
+ */
+
+/**
+ * @param {number} steps
+ * @param {number} arrLen
+ * @return {number}
+ */
+var numWays = function(steps, arrLen) {
+  const MOD = 1e9 + 7;
+  const maxPos = Math.min(steps, arrLen - 1);
+  let dp = new Array(maxPos + 1).fill(0);
+  dp[0] = 1;
+
+  for (let step = 1; step <= steps; step++) {
+    const prev = dp;
+    dp = new Array(maxPos + 1).fill(0);
+    for (let pos = 0; pos <= maxPos; pos++) {
+      dp[pos] = prev[pos];
+      if (pos > 0) dp[pos] = (dp[pos] + prev[pos - 1]) % MOD;
+      if (pos < maxPos) dp[pos] = (dp[pos] + prev[pos + 1]) % MOD;
+    }
+  }
+
+  return dp[0];
+};