From fdbf72a5bcd437182494a3896711e05502d4e10b Mon Sep 17 00:00:00 2001
From: Chiranjeev <6258860@gmail.com>
Date: Wed, 27 Oct 2021 17:08:48 +0530
Subject: [PATCH] added nth-tribonacci problem

---
 Leetcode/DP/N-th Tribonacci Number.cpp | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 Leetcode/DP/N-th Tribonacci Number.cpp

diff --git a/Leetcode/DP/N-th Tribonacci Number.cpp b/Leetcode/DP/N-th Tribonacci Number.cpp
new file mode 100644
index 0000000..09499d9
--- /dev/null
+++ b/Leetcode/DP/N-th Tribonacci Number.cpp	
@@ -0,0 +1,25 @@
+/* 
+	Approach Used: Bottom-up Dynamic Programming
+
+	F(N) = F(N-1) + F(N-2) + F(N-3), so using the fact that we only need last three values, we can build up the solution taking first 3 values of F(0) = 0, F(1) = 1, F(2) = 1, and build the solution upto N using previous three values.
+
+	Time Complexity: O(n)
+	Space Complexity: O(1)
+
+ */
+
+class Solution {
+public:
+    int tribonacci(int n) {
+        if(n == 0)return 0;
+        int first = 0, second = 1, third = 1;
+        for(int i=3; i <= n; i++){
+            int fourth = first + second + third;
+            first = second;
+            second = third;
+            third = fourth;
+        }
+        
+        return third;
+    }
+};
\ No newline at end of file