70_Climb_Stairs

Week2/70_Climbing_Stairs.cpp

@@ -0,0 +1,23 @@
+class Solution {
+public:
+    int climbStairs(int n) {
+	// We will use dp approach here.
+	// To the i th level we can get either from i-1 or i-2 level, thus ways to get to ith is the sum of mentioned 2.
+	// Initial state: 1 way to get to the 1st level, 1 way of getting to 0th level.
+	// It is Fibonacci sequence.
+
+        int curLevelWaysCount = 1, prevLevelWaysCount = 1;
+        for (int level = 2; level <= n; ++level) {
+            curLevelWaysCount += prevLevelWaysCount;
+            prevLevelWaysCount = curLevelWaysCount - prevLevelWaysCount;
+        }
+        return curLevelWaysCount;
+    }
+};
+
+/* 
+	n - number of stair levels.
+	Time Complexity T = O(n).
+	Memory complexity M = O(n).
+
+*/