Merge pull request #13 from lxmn22nov/lxmn3

Java: Memoization

Author: akscoder082003

Java/Memoization/NthTribonacciNumber.java

@@ -0,0 +1,33 @@
+/*
+ * PROBLEM: 1137
+ * 
+ * The Tribonacci sequence Tn is defined as follows: 
+
+T0 = 0, T1 = 1, T2 = 1, and Tn+3 = Tn + Tn+1 + Tn+2 for n >= 0.
+
+Given n, return the value of Tn.
+
+Example 1:
+Input: n = 4
+Output: 4
+Explanation:
+T_3 = 0 + 1 + 1 = 2
+T_4 = 1 + 1 + 2 = 4
+
+Example 2:
+Input: n = 25
+Output: 1389537
+ */
+public class NthTribonacciNumber {
+    public int tribonacci(int n) {
+        if (n <= 2) {
+            return n == 0 ? 0 : 1;
+        }
+        int[] dp = new int[n + 1];
+        dp[1] = dp[2] = 1;
+        for (int i = 3; i <= n; i++) {
+            dp[i] = dp[i - 2] + dp[i - 1] + dp[i - 3];
+        }
+        return dp[n];
+    }
+}