Add solution and test-cases for problem 756

Author: 0xff-dev

leetcode/701-800/0756.Pyramid-Transition-Matrix/1.jpg

@@ -1,28 +1,38 @@
 # [756.Pyramid Transition Matrix][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
+You are stacking blocks to form a pyramid. Each block has a color, which is represented by a single letter. Each row of blocks contains **one less block** than the row beneath it and is centered on top.
+
+To make the pyramid aesthetically pleasing, there are only specific **triangular patterns** that are allowed. A triangular pattern consists of a **single block** stacked on top of **two blocks**. The patterns are given as a list of three-letter strings `allowed`, where the first two characters of a pattern represent the left and right bottom blocks respectively, and the third character is the top block.
+
+- For example, `"ABC"` represents a triangular pattern with a `'C'` block stacked on top of an `'A'` (left) and `'B'` (right) block. Note that this is different from `"BAC"` where `'B'` is on the left bottom and `'A'` is on the right bottom.
+
+You start with a bottom row of blocks `bottom`, given as a single string, that you **must** use as the base of the pyramid.
 
-**Example 1:**
+Given `bottom` and `allowed`, return true if you can build the pyramid all the way to the top such that **every triangular pattern** in the pyramid is in `allowed`, or `false` otherwise.
+
+**Example 1:**  
+
+![1](./1.jpg)
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: bottom = "BCD", allowed = ["BCC","CDE","CEA","FFF"]
+Output: true
+Explanation: The allowed triangular patterns are shown on the right.
+Starting from the bottom (level 3), we can build "CE" on level 2 and then build "A" on level 1.
+There are three triangular patterns in the pyramid, which are "BCC", "CDE", and "CEA". All are allowed.
 ```
 
-## 题意
-> ...
+**Example 2:**  
 
-## 题解
+![2](./2.jpg)
 
-### 思路1
-> ...
-Pyramid Transition Matrix
-```go
 ```
-
+Input: bottom = "AAAA", allowed = ["AAB","AAC","BCD","BBE","DEF"]
+Output: false
+Explanation: The allowed triangular patterns are shown on the right.
+Starting from the bottom (level 4), there are multiple ways to build level 3, but trying all the possibilites, you will get always stuck before building level 1.
+```
 
 ## 结语
 

leetcode/701-800/0756.Pyramid-Transition-Matrix/2.jpg

@@ -1,5 +1,43 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+func Solution(bottom string, allowed []string) bool {
+	allowedMap := make(map[[2]byte][]byte)
+	for _, pattern := range allowed {
+		key := [2]byte{pattern[0], pattern[1]}
+		allowedMap[key] = append(allowedMap[key], pattern[2])
+	}
+
+	var canBuild func(string) bool
+	canBuild = func(current string) bool {
+		if len(current) == 1 {
+			return true
+		}
+
+		var nextLayers []string
+
+		var backtrack func(int, []byte)
+		backtrack = func(index int, path []byte) {
+			if index == len(current)-1 {
+				nextLayers = append(nextLayers, string(path))
+				return
+			}
+			pair := [2]byte{current[index], current[index+1]}
+			if tops, exists := allowedMap[pair]; exists {
+				for _, top := range tops {
+					backtrack(index+1, append(path, top))
+				}
+			}
+		}
+
+		backtrack(0, []byte{})
+
+		for _, nextLayer := range nextLayers {
+			if canBuild(nextLayer) {
+				return true
+			}
+		}
+		return false
+	}
+
+	return canBuild(bottom)
 }

leetcode/701-800/0756.Pyramid-Transition-Matrix/README.md

@@ -9,31 +9,31 @@ import (
 func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
-		name   string
-		inputs bool
-		expect bool
+		name    string
+		bottom  string
+		allowed []string
+		expect  bool
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", "BCD", []string{"BCC", "CDE", "CEA", "FFF"}, true},
+		{"TestCase2", "AAAA", []string{"AAB", "AAC", "BCD", "BBE", "DEF"}, false},
 	}
 
 	//	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.bottom, c.allowed)
 			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.bottom, c.allowed)
 			}
 		})
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }