Merge pull request #670 from 0xff-dev/779

Add solution and test-cases for problem 779

leetcode/701-800/0779.K-th-Symbol-in-Grammar/README.md

@@ -1,28 +1,39 @@
 # [779.K-th Symbol in Grammar][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
+We build a table of `n` rows (**1-indexed**). We start by writing `0` in the 1<sup>st</sup> row. Now in every subsequent row, we look at the previous row and replace each occurrence of `0` with `01`, and each occurrence of `1` with `10`.
+
+- For example, for `n = 3`, the 1<sup>st</sup> row is `0`, the 2<sup>nd</sup> row is `01`, and the 3<sup>rd</sup> row is `0110`.
+
+Given two integer `n` and `k`, return the k<sup>th<sup> (**1-indexed**) symbol in the n<sup>th</sup> row of a table of `n` rows.
 
 **Example 1:**
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: n = 1, k = 1
+Output: 0
+Explanation: row 1: 0
 ```
 
-## 题意
-> ...
-
-## 题解
+**Example 2:**
 
-### 思路1
-> ...
-K-th Symbol in Grammar
-```go
 ```
+Input: n = 2, k = 1
+Output: 0
+Explanation: 
+row 1: 0
+row 2: 01
+```
+
+**Example 3:**
 
+```
+Input: n = 2, k = 2
+Output: 1
+Explanation: 
+row 1: 0
+row 2: 01
+```
 
 ## 结语
 

leetcode/701-800/0779.K-th-Symbol-in-Grammar/Solution.go

@@ -1,5 +1,34 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+/*
+0
+0          1
+0    1     1     0
+0 1  1  0  1  0  0  1
+1 2  3  4  5  6  7  8
+*/
+func Solution(n int, k int) int {
+	nn := n
+	path := make([]int, 0)
+	for nn > 0 {
+		path = append(path, k)
+		if k&1 == 1 {
+			k++
+		}
+		k /= 2
+		nn--
+	}
+	ans := 0
+	for i := len(path) - 2; i >= 0; i-- {
+		a, b := 0, 1
+		if ans != 0 {
+			a, b = 1, 0
+		}
+		if path[i] == path[i+1]*2 {
+			ans = b
+			continue
+		}
+		ans = a
+	}
+	return ans
 }

leetcode/701-800/0779.K-th-Symbol-in-Grammar/Solution_test.go

@@ -10,30 +10,31 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
-		expect bool
+		n, k   int
+		expect int
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", 1, 1, 0},
+		{"TestCase2", 2, 1, 0},
+		{"TestCase3", 2, 2, 1},
+		{"TestCase4", 28, 472, 1},
 	}
 
 	//	开始测试
 	for i, c := range cases {
 		t.Run(c.name+" "+strconv.Itoa(i), func(t *testing.T) {
-			got := Solution(c.inputs)
+			got := Solution(c.n, c.k)
 			if !reflect.DeepEqual(got, c.expect) {
-				t.Fatalf("expected: %v, but got: %v, with inputs: %v",
-					c.expect, got, c.inputs)
+				t.Fatalf("expected: %v, but got: %v, with inputs: %v %v",
+					c.expect, got, c.n, c.k)
 			}
 		})
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }