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

Author: everthis

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

@@ -0,0 +1,22 @@
+/**
+ * @param {number} steps
+ * @param {number} arrLen
+ * @return {number}
+ */
+const numWays = function (steps, arrLen) {
+  const MOD = 10 ** 9 + 7
+  const memo = Array.from({ length: (steps >> 1) + 1 }, () =>
+    Array(steps + 1).fill(-1)
+  )
+  return dp(0, steps)
+  function dp(i, steps) {
+    if (steps === 0 && i === 0) return 1
+    if (i < 0 || i >= arrLen || steps === 0 || i > steps) return 0
+    if (memo[i][steps] !== -1) return memo[i][steps]
+    return (memo[i][steps] =
+      ((dp(i + 1, steps - 1) % MOD) +
+        (dp(i - 1, steps - 1) % MOD) +
+        (dp(i, steps - 1) % MOD)) %
+      MOD)
+  }
+}