merge: Add TribonacciNumber in dp (#839)

Dynamic-Programming/TribonacciNumber.js

@@ -0,0 +1,20 @@
+/**
+ * @function Tribonacci
+ * @description Tribonacci is the sum of previous three tribonacci numbers.
+ * @param {Integer} n - The input integer
+ * @return {Integer} tribonacci of n.
+ * @see [Tribonacci_Numbers](https://www.geeksforgeeks.org/tribonacci-numbers/)
+ */
+const tribonacci = (n) => {
+  // creating array to store previous tribonacci numbers
+  const dp = new Array(n + 1)
+  dp[0] = 0
+  dp[1] = 1
+  dp[2] = 1
+  for (let i = 3; i <= n; i++) {
+    dp[i] = dp[i - 1] + dp[i - 2] + dp[i - 3]
+  }
+  return dp[n]
+}
+
+export { tribonacci }