climbing-stairs solution

Author: togo26

climbing-stairs/togo26.js

@@ -0,0 +1,28 @@
+/**
+ * @param {number} n
+ * @return {number}
+ */
+
+// TC: O(n) / SC: O(n)
+var climbStairs = function (n) {
+  if (n <= 3) return n;
+  const dp = [1, 2, 3];
+  for (let i = 3; i < n; i++) {
+    dp[i] = dp[i - 2] + dp[i - 1];
+  }
+
+  return dp[dp.length - 1];
+};
+
+// TC: O(n) / SC: O(1)
+var climbStairs = function (n) {
+  let temp,
+    pre1 = 1,
+    pre2 = 1;
+  for (let i = 1; i < n; i++) {
+    temp = pre2;
+    pre2 = pre1 + pre2;
+    pre1 = temp;
+  }
+  return pre2;
+};