规范格式

leetcode/0756.Pyramid-Transition-Matrix/756. Pyramid Transition Matrix.go

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+package leetcode
+
+func pyramidTransition(bottom string, allowed []string) bool {
+	pyramid := make(map[string][]string)
+	for _, v := range allowed {
+		pyramid[v[:len(v)-1]] = append(pyramid[v[:len(v)-1]], string(v[len(v)-1]))
+	}
+	return dfsT(bottom, "", pyramid)
+}
+
+func dfsT(bottom, above string, pyramid map[string][]string) bool {
+	if len(bottom) == 2 && len(above) == 1 {
+		return true
+	}
+	if len(bottom) == len(above)+1 {
+		return dfsT(above, "", pyramid)
+	}
+	base := bottom[len(above) : len(above)+2]
+	if data, ok := pyramid[base]; ok {
+		for _, key := range data {
+			if dfsT(bottom, above+key, pyramid) {
+				return true
+			}
+		}
+	}
+	return false
+}

leetcode/0756.Pyramid-Transition-Matrix/756. Pyramid Transition Matrix_test.go

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+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question756 struct {
+	para756
+	ans756
+}
+
+// para 是参数
+// one 代表第一个参数
+type para756 struct {
+	b string
+	a []string
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans756 struct {
+	one bool
+}
+
+func Test_Problem756(t *testing.T) {
+
+	qs := []question756{
+
+		question756{
+			para756{"BCD", []string{"BCG", "CDE", "GEA", "FFF"}},
+			ans756{true},
+		},
+
+		question756{
+			para756{"AABA", []string{"AAA", "AAB", "ABA", "ABB", "BAC"}},
+			ans756{false},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 756------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans756, q.para756
+		fmt.Printf("【input】:%v       【output】:%v\n", p, pyramidTransition(p.b, p.a))
+	}
+	fmt.Printf("\n\n\n")
+}

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

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+# [756. Pyramid Transition Matrix](https://leetcode.com/problems/pyramid-transition-matrix/)
+
+
+## 题目:
+
+We are stacking blocks to form a pyramid. Each block has a color which is a one letter string.
+
+We are allowed to place any color block `C` on top of two adjacent blocks of colors `A` and `B`, if and only if `ABC` is an allowed triple.
+
+We start with a bottom row of `bottom`, represented as a single string. We also start with a list of allowed triples `allowed`. Each allowed triple is represented as a string of length 3.
+
+Return true if we can build the pyramid all the way to the top, otherwise false.
+
+**Example 1:**
+
+    Input: bottom = "BCD", allowed = ["BCG", "CDE", "GEA", "FFF"]
+    Output: true
+    Explanation:
+    We can stack the pyramid like this:
+        A
+       / \
+      G   E
+     / \ / \
+    B   C   D
+    
+    We are allowed to place G on top of B and C because BCG is an allowed triple.  Similarly, we can place E on top of C and D, then A on top of G and E.
+
+**Example 2:**
+
+    Input: bottom = "AABA", allowed = ["AAA", "AAB", "ABA", "ABB", "BAC"]
+    Output: false
+    Explanation:
+    We can't stack the pyramid to the top.
+    Note that there could be allowed triples (A, B, C) and (A, B, D) with C != D.
+
+**Note:**
+
+1. `bottom` will be a string with length in range `[2, 8]`.
+2. `allowed` will have length in range `[0, 200]`.
+3. Letters in all strings will be chosen from the set `{'A', 'B', 'C', 'D', 'E', 'F', 'G'}`.
+
+
+## 题目大意
+
+现在，我们用一些方块来堆砌一个金字塔。 每个方块用仅包含一个字母的字符串表示，例如 “Z”。使用三元组表示金字塔的堆砌规则如下：
+
+(A, B, C) 表示，“C” 为顶层方块，方块 “A”、“B” 分别作为方块 “C” 下一层的的左、右子块。当且仅当(A, B, C)是被允许的三元组，我们才可以将其堆砌上。
+
+初始时，给定金字塔的基层 bottom，用一个字符串表示。一个允许的三元组列表 allowed，每个三元组用一个长度为 3 的字符串表示。如果可以由基层一直堆到塔尖返回 true，否则返回 false。
+
+
+
+## 解题思路
+
+- 这一题是一道 DFS 的题目。题目给出金字塔的底座字符串。然后还会给一个字符串数组，字符串数组里面代表的字符串的砖块。砖块是 3 个字符串组成的。前两个字符代表的是砖块的底边，后一个字符代表的是砖块的顶部。问给出的字符能拼成一个金字塔么？金字塔的特点是顶端就一个字符。  
+
+- 这一题用 DFS 深搜每个砖块，从底层砖块开始逐渐往上层码。每递归一层，新一层底部的砖块都会变。当递归到了一层底部只有 2 个字符，顶部只有一个字符的时候，就到金字塔顶端了，就算是完成了。这一题为了挑选合适的砖块，需要把每个砖块底部的 2 个字符作为 key 放进 map 中，加速查找。题目中也给出了特殊情况，相同底部可能存在多种砖块，所以一个 key 可能对应多个 value 的情况，即可能存在多个顶部砖块的情况。这种情况在递归遍历中需要考虑。