From a5f906f309f893ece2ea729b798c05003365eb6e Mon Sep 17 00:00:00 2001
From: YDZ <ydz627@gmail.com>
Date: Fri, 13 Dec 2019 18:35:15 +0800
Subject: [PATCH] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=20problem=201137?=
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---
 .../1137. N-th Tribonacci Number.go           | 13 ++++
 .../1137. N-th Tribonacci Number_test.go      | 62 +++++++++++++++++++
 .../1137. N-th Tribonacci Number/README.md    | 50 +++++++++++++++
 3 files changed, 125 insertions(+)
 create mode 100644 Algorithms/1137. N-th Tribonacci Number/1137. N-th Tribonacci Number.go
 create mode 100644 Algorithms/1137. N-th Tribonacci Number/1137. N-th Tribonacci Number_test.go
 create mode 100755 Algorithms/1137. N-th Tribonacci Number/README.md

diff --git a/Algorithms/1137. N-th Tribonacci Number/1137. N-th Tribonacci Number.go b/Algorithms/1137. N-th Tribonacci Number/1137. N-th Tribonacci Number.go
new file mode 100644
index 00000000..d31d0c09
--- /dev/null
+++ b/Algorithms/1137. N-th Tribonacci Number/1137. N-th Tribonacci Number.go	
@@ -0,0 +1,13 @@
+package leetcode
+
+func tribonacci(n int) int {
+	if n < 2 {
+		return n
+	}
+	trib, prev, prev2 := 1, 1, 0
+	for n > 2 {
+		trib, prev, prev2 = trib+prev+prev2, trib, prev
+		n--
+	}
+	return trib
+}
diff --git a/Algorithms/1137. N-th Tribonacci Number/1137. N-th Tribonacci Number_test.go b/Algorithms/1137. N-th Tribonacci Number/1137. N-th Tribonacci Number_test.go
new file mode 100644
index 00000000..3b0bce88
--- /dev/null
+++ b/Algorithms/1137. N-th Tribonacci Number/1137. N-th Tribonacci Number_test.go	
@@ -0,0 +1,62 @@
+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question1137 struct {
+	para1137
+	ans1137
+}
+
+// para 是参数
+// one 代表第一个参数
+type para1137 struct {
+	one int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans1137 struct {
+	one int
+}
+
+func Test_Problem1137(t *testing.T) {
+
+	qs := []question1137{
+
+		question1137{
+			para1137{1},
+			ans1137{1},
+		},
+
+		question1137{
+			para1137{2},
+			ans1137{1},
+		},
+
+		question1137{
+			para1137{3},
+			ans1137{2},
+		},
+
+		question1137{
+			para1137{4},
+			ans1137{4},
+		},
+
+		question1137{
+			para1137{25},
+			ans1137{1389537},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 1137------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans1137, q.para1137
+		fmt.Printf("【input】:%v       【output】:%v\n", p, tribonacci(p.one))
+	}
+	fmt.Printf("\n\n\n")
+}
diff --git a/Algorithms/1137. N-th Tribonacci Number/README.md b/Algorithms/1137. N-th Tribonacci Number/README.md
new file mode 100755
index 00000000..03cfa081
--- /dev/null
+++ b/Algorithms/1137. N-th Tribonacci Number/README.md	
@@ -0,0 +1,50 @@
+# [1137. N-th Tribonacci Number](https://leetcode.com/problems/n-th-tribonacci-number/)
+
+
+## 题目:
+
+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
+
+**Constraints:**
+
+- `0 <= n <= 37`
+- The answer is guaranteed to fit within a 32-bit integer, ie. `answer <= 2^31 - 1`.
+
+
+## 题目大意
+
+
+泰波那契序列 Tn 定义如下： 
+
+T0 = 0, T1 = 1, T2 = 1, 且在 n >= 0 的条件下 Tn+3 = Tn + Tn+1 + Tn+2
+
+给你整数 n，请返回第 n 个泰波那契数 Tn 的值。
+
+提示：
+
+- 0 <= n <= 37
+- 答案保证是一个 32 位整数，即 answer <= 2^31 - 1。
+
+
+
+## 解题思路
+
+- 求泰波那契数列中的第 n 个数。
+- 简单题，按照题意定义计算即可。