✨ solve 1137

1137.cpp

@@ -0,0 +1,28 @@
+// https://leetcode.com/problems/n-th-tribonacci-number/
+
+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution {
+ public:
+  int tribonacci(int n) {
+    int a = 0;
+    int b = 1;
+    int c = 1;
+
+    for (int i = 2; i < n; ++i) {
+      int bb = b;
+      c = a + b + c;
+      b = c - (b + a);
+      a = bb;
+    }
+
+    if (n == 0) {
+      return a;
+    } else if (n == 1) {
+      return b;
+    } else {
+      return c;
+    }
+  }
+};