Merge pull request DaleStudy#2121 from ymir0804/main

[ymir0804] WEEK 03 solutions

Author: TonyKim9401

climbing-stairs/ymir0804.java

@@ -0,0 +1,22 @@
+class Solution {
+    public int climbStairs(int n) {
+        int result = 0;
+        int first = 1;
+        int second = 2;
+        int third = 3;
+        if (n == 1) {
+            return first;
+        } else if (n == 2) {
+            return second;
+        } else if (n == 3) {
+            return third;
+        }
+
+        for (int i = 4; i <= n; i++) {
+            result = second + third;
+            second = third;
+            third = result;
+        }
+        return result;
+    }
+}