Add solution and test-cases for problem 1718

Author: 0xff-dev

leetcode/1701-1800/1718.Construct-the-Lexicographically-Largest-Valid-Sequence/README.md

@@ -1,28 +1,32 @@
 # [1718.Construct the Lexicographically Largest Valid Sequence][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
+Given an integer `n`, find a sequence that satisfies all of the following:
+
+- The integer `1` occurs once in the sequence.
+- Each integer between `2` and `n` occurs twice in the sequence.
+- For every integer `i` between `2` and `n`, the **distance** between the two occurrences of `i` is exactly `i`.
+
+The **distance** between two numbers on the sequence, `a[i]` and `a[j]`, is the absolute difference of their indices, `|j - i|`.
+
+Return the **lexicographically largest** sequence. It is guaranteed that under the given constraints, there is always a solution.
+
+A sequence `a` is lexicographically larger than a sequence `b` (of the same length) if in the first position where `a` and `b` differ, sequence a has a number greater than the corresponding number in `b`. For example, `[0,1,9,0]` is lexicographically larger than `[0,1,5,6]` because the first position they differ is at the third number, and `9` is greater than `5`.
 
 **Example 1:**
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: n = 3
+Output: [3,1,2,3,2]
+Explanation: [2,3,2,1,3] is also a valid sequence, but [3,1,2,3,2] is the lexicographically largest valid sequence.
 ```
 
-## 题意
-> ...
-
-## 题解
+**Example 2:**
 
-### 思路1
-> ...
-Construct the Lexicographically Largest Valid Sequence
-```go
 ```
-
+Input: n = 5
+Output: [5,3,1,4,3,5,2,4,2]
+```
 
 ## 结语
 

leetcode/1701-1800/1718.Construct-the-Lexicographically-Largest-Valid-Sequence/Solution.go

@@ -1,5 +1,43 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+func Solution(n int) []int {
+	l := 2*n - 1
+	res := make([]int, l)
+	used := make([]bool, n+1)
+	var dfs func(int) bool
+	dfs = func(start int) bool {
+		if start == l {
+			return true
+		}
+		if res[start] != 0 {
+			return dfs(start + 1)
+		}
+
+		for s := n; s >= 1; s-- {
+			if used[s] {
+				continue
+			}
+			res[start] = s
+			used[s] = true
+			if s == 1 {
+				if dfs(start + 1) {
+					return true
+				}
+			} else {
+				if end := start + s; end < l && res[end] == 0 {
+					res[end] = s
+					if dfs(start + 1) {
+						return true
+					}
+					res[end] = 0
+				}
+			}
+			res[start] = 0
+			used[s] = false
+		}
+		return false
+	}
+
+	dfs(0)
+	return res
 }

leetcode/1701-1800/1718.Construct-the-Lexicographically-Largest-Valid-Sequence/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", 3, []int{3, 1, 2, 3, 2}},
+		{"TestCase2", 5, []int{5, 3, 1, 4, 3, 5, 2, 4, 2}},
 	}
 
 	//	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() {
 }