Merge pull request #907 from 0xff-dev/873

Add solution and test-cases for problem 873

Author: 6boris

leetcode/801-900/0873.Length-of-Longest-Fibonacci-Subsequence/README.md

@@ -1,28 +1,30 @@
 # [873.Length of Longest Fibonacci Subsequence][title]
 
-> [!WARNING|style:flat]
-> This question is temporarily unanswered if you have good ideas. Welcome to [Create Pull Request PR](https://github.com/kylesliu/awesome-golang-algorithm)
-
 ## Description
+A sequence `x1, x2, ..., xn` is Fibonacci-like if:
+
+- `n >= 3`
+- `xi + xi+1 == xi+2` for all `i + 2 <= n`
+
+Given a **strictly increasing** array `arr` of positive integers forming a sequence, return the **length** of the longest Fibonacci-like subsequence of `arr`. If one does not exist, return `0`.
+
+A **subsequence** is derived from another sequence `arr` by deleting any number of elements (including none) from `arr`, without changing the order of the remaining elements. For example, `[3, 5, 8]` is a subsequence of `[3, 4, 5, 6, 7, 8]`.
 
 **Example 1:**
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: arr = [1,2,3,4,5,6,7,8]
+Output: 5
+Explanation: The longest subsequence that is fibonacci-like: [1,2,3,5,8].
 ```
 
-## 题意
-> ...
+**Example 2:**
 
-## 题解
-
-### 思路1
-> ...
-Length of Longest Fibonacci Subsequence
-```go
 ```
-
+Input: arr = [1,3,7,11,12,14,18]
+Output: 3
+Explanation: The longest subsequence that is fibonacci-like: [1,11,12], [3,11,14] or [7,11,18].
+```
 
 ## 结语
 

leetcode/801-900/0873.Length-of-Longest-Fibonacci-Subsequence/Solution.go

@@ -1,5 +1,28 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+func Solution(arr []int) int {
+	nums := make(map[int]struct{})
+	for _, n := range arr {
+		nums[n] = struct{}{}
+	}
+	var try func(int, int, *int)
+	try = func(a, b int, c *int) {
+		_, ok := nums[a+b]
+		if !ok {
+			return
+		}
+		*c++
+		try(b, a+b, c)
+	}
+	ans := 0
+	for i := 0; i < len(arr)-1; i++ {
+		for j := i + 1; j < len(arr); j++ {
+			c := 0
+			try(arr[i], arr[j], &c)
+			if c != 0 {
+				ans = max(ans, c+2)
+			}
+		}
+	}
+	return ans
 }

leetcode/801-900/0873.Length-of-Longest-Fibonacci-Subsequence/Solution_test.go

@@ -10,12 +10,11 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
-		expect bool
+		inputs []int
+		expect int
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", []int{1, 2, 3, 4, 5, 6, 7, 8}, 5},
+		{"TestCase2", []int{1, 3, 7, 11, 12, 14, 18}, 3},
 	}
 
 	//	开始测试
@@ -30,10 +29,10 @@ func TestSolution(t *testing.T) {
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }