Paint Fence

Author: sachuverma

Leetcode Daily Challenge/August-2021/Paint Fence.cpp

@@ -0,0 +1,55 @@
+/*
+Paint Fence
+===========
+
+You are painting a fence of n posts with k different colors. You must paint the posts following these rules:
+
+Every post must be painted exactly one color.
+There cannot be three or more consecutive posts with the same color.
+Given the two integers n and k, return the number of ways you can paint the fence.
+
+Example 1:
+Input: n = 3, k = 2
+Output: 6
+Explanation: All the possibilities are shown.
+Note that painting all the posts red or all the posts green is invalid because there cannot be three posts in a row with the same color.
+
+Example 2:
+Input: n = 1, k = 1
+Output: 1
+
+Example 3:
+Input: n = 7, k = 2
+Output: 42
+ 
+Constraints:
+1 <= n <= 50
+1 <= k <= 105
+The testcases are generated such that the answer is in the range [0, 231 - 1] for the given n and k.
+*/
+
+class Solution
+{
+public:
+    int numWays(int n, int k)
+    {
+        if (n == 1)
+            return k;
+        if (n == 2)
+            return k * k;
+
+        int prevTwo = k;
+        int prevOne = k * k;
+
+        int ans = prevTwo;
+
+        for (int i = 3; i <= n; ++i)
+        {
+            ans = (k - 1) * prevOne + (k - 1) * prevTwo;
+            prevTwo = prevOne;
+            prevOne = ans;
+        }
+
+        return ans;
+    }
+};

Leetcode Daily Challenge/August-2021/README.md

@@ -10,6 +10,7 @@
 | 5.  | [Stone Game](https://leetcode.com/explore/challenge/card/august-leetcoding-challenge-2021/613/week-1-august-1st-august-7th/3870/)                               |                 [cpp](./05.%20Stone%20Game.cpp)                 |
 | 6.  | [N-ary Tree Level Order Traversal](https://leetcode.com/explore/challenge/card/august-leetcoding-challenge-2021/613/week-1-august-1st-august-7th/3871/)         |   [cpp](./06.%20N-ary%20Tree%20Level%20Order%20Traversal.cpp)   |
 | 7.  | [Palindrome Partitioning II](https://leetcode.com/explore/challenge/card/august-leetcoding-challenge-2021/613/week-1-august-1st-august-7th/3872/)               |        [cpp](./07.%20Palindrome%20Partitioning%20II.cpp)        |
+|     | [Paint Fence](https://leetcode.com/explore/challenge/card/august-leetcoding-challenge-2021/614/week-2-august-8th-august-14th/3873/)                             |                   [cpp](./Paint%20Fence.cpp)                    |
 | 9.  | [Add Strings](https://leetcode.com/explore/challenge/card/august-leetcoding-challenge-2021/614/week-2-august-8th-august-14th/3875/)                             |                [cpp](./09.%20Add%20Strings.cpp)                 |
 | 10. | [Flip String to Monotone Increasing](https://leetcode.com/explore/challenge/card/august-leetcoding-challenge-2021/614/week-2-august-8th-august-14th/3876/)      |  [cpp](./10.%20Flip%20String%20to%20Monotone%20Increasing.cpp)  |
 | 11. | [Array of Doubled Pairs](https://leetcode.com/explore/challenge/card/august-leetcoding-challenge-2021/614/week-2-august-8th-august-14th/3877/)                  |         [cpp](./11.%20Array%20of%20Doubled%20Pairs.cpp)         |