solve: climbing stairs

Author: sounmind

climbing-stairs/evan.js

@@ -0,0 +1,30 @@
+/**
+ * @param {number} n
+ * @return {number}
+ */
+var climbStairs = function (n) {
+  if (n <= 2) {
+    return n;
+  }
+
+  let [firstStair, secondStair] = [1, 2];
+  let thirdStair;
+
+  for (let i = 3; i <= n; i++) {
+    thirdStair = firstStair + secondStair;
+
+    [firstStair, secondStair] = [secondStair, thirdStair];
+  }
+
+  return thirdStair;
+};
+
+// Time Complexity: O(n)
+// Reason: The function uses a loop that iterates from 3 to n,
+//         which means it runs in linear time with respect to n.
+
+// Space Complexity: O(1)
+// Reason: The function uses a fixed amount of extra space
+//         (a few integer variables: first, second, and third).
+//         It does not use any additional data structures
+//         that grow with the input size n.