add climbStairs solution

Author: HoonDongKang

climbing-stairs/HoonDongKang.ts

@@ -0,0 +1,44 @@
+/**
+ * [Problem]: [70] Climbing Stairs
+ * (https://leetcode.com/problems/climbing-stairs/description/)
+ */
+
+function climbStairs(n: number): number {
+    // 시간복잡도 O(n)
+    // 공간복잡도 O(n)
+    function dpFunc(n: number): number {
+        if (n <= 0) return 0;
+
+        let dpArr: number[] = new Array(n);
+        dpArr[0] = 1;
+        dpArr[1] = 2;
+
+        for (let i = 2; i < n; i++) {
+            dpArr[i] = dpArr[i - 1] + dpArr[i - 2];
+        }
+
+        return dpArr[n - 1];
+    }
+
+    // 시간복잡도 O(n)
+    // 공간복잡도 O(1)
+    function dpOptimizedFunc(n: number): number {
+        if (n <= 0) return 0;
+        if (n === 1) return 1;
+        if (n === 2) return 2;
+
+        let prev1 = 1;
+        let prev2 = 2;
+
+        for (let i = 3; i < n + 1; i++) {
+            let currentValue = prev1 + prev2;
+
+            prev1 = prev2;
+            prev2 = currentValue;
+        }
+
+        return prev2;
+    }
+
+    return dpOptimizedFunc(n);
+}