Add solution 823

2025-07-06 01:15:57 +08:00 · 2021-03-13 21:21:21 +08:00
parent 8bb84f2edc
commit 943d558ca8
26 changed files with 1029 additions and 662 deletions
--- a/leetcode/0823.Binary-Trees-With-Factors/823.
+++ b/leetcode/0823.Binary-Trees-With-Factors/823.
@ -0,0 +1,70 @@
+package leetcode
+
+import (
+	"sort"
+)
+
+const mod = 1e9 + 7
+
+// 解法一 DFS
+func numFactoredBinaryTrees(arr []int) int {
+	sort.Ints(arr)
+	numDict := map[int]bool{}
+	for _, num := range arr {
+		numDict[num] = true
+	}
+	dict, res := make(map[int][][2]int), 0
+	for i, num := range arr {
+		for j := i; j < len(arr) && num*arr[j] <= arr[len(arr)-1]; j++ {
+			tmp := num * arr[j]
+			if !numDict[tmp] {
+				continue
+			}
+			dict[tmp] = append(dict[tmp], [2]int{num, arr[j]})
+		}
+	}
+	cache := make(map[int]int)
+	for _, num := range arr {
+		res = (res + dfs(num, dict, cache)) % mod
+	}
+	return res
+}
+
+func dfs(num int, dict map[int][][2]int, cache map[int]int) int {
+	if val, ok := cache[num]; ok {
+		return val
+	}
+	res := 1
+	for _, tuple := range dict[num] {
+		a, b := tuple[0], tuple[1]
+		x, y := dfs(a, dict, cache), dfs(b, dict, cache)
+		tmp := x * y
+		if a != b {
+			tmp *= 2
+		}
+		res = (res + tmp) % mod
+	}
+	cache[num] = res
+	return res
+}
+
+// 解法二 DP
+func numFactoredBinaryTrees1(arr []int) int {
+	dp := make(map[int]int)
+	sort.Ints(arr)
+	for i, curNum := range arr {
+		for j := 0; j < i; j++ {
+			factor := arr[j]
+			quotient, remainder := curNum/factor, curNum%factor
+			if remainder == 0 {
+				dp[curNum] += dp[factor] * dp[quotient]
+			}
+		}
+		dp[curNum]++
+	}
+	totalCount := 0
+	for _, count := range dp {
+		totalCount += count
+	}
+	return totalCount % mod
+}
--- a/leetcode/0823.Binary-Trees-With-Factors/823.
+++ b/leetcode/0823.Binary-Trees-With-Factors/823.
@ -0,0 +1,47 @@
+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question823 struct {
+	para823
+	ans823
+}
+
+// para 是参数
+// one 代表第一个参数
+type para823 struct {
+	arr []int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans823 struct {
+	one int
+}
+
+func Test_Problem823(t *testing.T) {
+
+	qs := []question823{
+
+		{
+			para823{[]int{2, 4}},
+			ans823{3},
+		},
+
+		{
+			para823{[]int{2, 4, 5, 10}},
+			ans823{7},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 823------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans823, q.para823
+		fmt.Printf("【input】:%v       【output】:%v\n", p, numFactoredBinaryTrees(p.arr))
+	}
+	fmt.Printf("\n\n\n")
+}
--- a/leetcode/0823.Binary-Trees-With-Factors/README.md
+++ b/leetcode/0823.Binary-Trees-With-Factors/README.md
@ -0,0 +1,119 @@
+# [823. Binary Trees With Factors](https://leetcode.com/problems/binary-trees-with-factors/)
+
+
+## 题目
+
+Given an array of unique integers, `arr`, where each integer `arr[i]` is strictly greater than `1`.
+
+We make a binary tree using these integers, and each number may be used for any number of times. Each non-leaf node's value should be equal to the product of the values of its children.
+
+Return *the number of binary trees we can make*. The answer may be too large so return the answer **modulo** `109 + 7`.
+
+**Example 1:**
+
+```
+Input: arr = [2,4]
+Output: 3
+Explanation: We can make these trees: [2], [4], [4, 2, 2]
+```
+
+**Example 2:**
+
+```
+Input: arr = [2,4,5,10]
+Output: 7
+Explanation: We can make these trees: [2], [4], [5], [10], [4, 2, 2], [10, 2, 5], [10, 5, 2].
+```
+
+**Constraints:**
+
+- `1 <= arr.length <= 1000`
+- `2 <= arr[i] <= 10^9`
+
+## 题目大意
+
+给出一个含有不重复整数元素的数组，每个整数均大于 1。我们用这些整数来构建二叉树，每个整数可以使用任意次数。其中：每个非叶结点的值应等于它的两个子结点的值的乘积。满足条件的二叉树一共有多少个？返回的结果应模除 10 * 9 + 7。
+
+## 解题思路
+
+- 首先想到的是暴力解法，先排序，然后遍历所有节点，枚举两两乘积为第三个节点值的组合。然后枚举这些组合并构成树。这里计数的时候要注意，左右孩子如果不是对称的，左右子树相互对调又是一组解。但是这个方法超时了。原因是，暴力枚举了很多次重复的节点和组合。优化这里的方法就是把已经计算过的节点放入 `map` 中。这里有 2 层 `map`，第一层 `map` 记忆化的是两两乘积的组合，将父亲节点作为 `key`，左右 2 个孩子作为 `value`。第二层 `map` 记忆化的是以 `root` 为根节点此时二叉树的种类数，`key` 是 `root`，`value` 存的是种类数。这样优化以后，DFS 暴力解法可以 runtime beats 100%。
+- 另外一种解法是 DP。定义 `dp[i]` 代表以 `i` 为根节点的树的种类数。dp[i] 初始都是 1，因为所有节点自身可以形成为自身单个节点为 `root` 的树。同样需要先排序。状态转移方程是：
+
+    $$dp[i] = \sum_{j<i, k<i}^{}dp[j] * dp[k], j * k = i$$
+
+    最后将 `dp[]` 数组中所有结果累加取模即为最终结果，时间复杂度 O(n^2)，空间复杂度 O(n)。
+
+## 代码
+
+```go
+package leetcode
+
+import (
+	"sort"
+)
+
+const mod = 1e9 + 7
+
+// 解法一 DFS
+func numFactoredBinaryTrees(arr []int) int {
+	sort.Ints(arr)
+	numDict := map[int]bool{}
+	for _, num := range arr {
+		numDict[num] = true
+	}
+	dict, res := make(map[int][][2]int), 0
+	for i, num := range arr {
+		for j := i; j < len(arr) && num*arr[j] <= arr[len(arr)-1]; j++ {
+			tmp := num * arr[j]
+			if !numDict[tmp] {
+				continue
+			}
+			dict[tmp] = append(dict[tmp], [2]int{num, arr[j]})
+		}
+	}
+	cache := make(map[int]int)
+	for _, num := range arr {
+		res = (res + dfs(num, dict, cache)) % mod
+	}
+	return res
+}
+
+func dfs(num int, dict map[int][][2]int, cache map[int]int) int {
+	if val, ok := cache[num]; ok {
+		return val
+	}
+	res := 1
+	for _, tuple := range dict[num] {
+		a, b := tuple[0], tuple[1]
+		x, y := dfs(a, dict, cache), dfs(b, dict, cache)
+		tmp := x * y
+		if a != b {
+			tmp *= 2
+		}
+		res = (res + tmp) % mod
+	}
+	cache[num] = res
+	return res
+}
+
+// 解法二 DP
+func numFactoredBinaryTrees1(arr []int) int {
+	dp := make(map[int]int)
+	sort.Ints(arr)
+	for i, curNum := range arr {
+		for j := 0; j < i; j++ {
+			factor := arr[j]
+			quotient, remainder := curNum/factor, curNum%factor
+			if remainder == 0 {
+				dp[curNum] += dp[factor] * dp[quotient]
+			}
+		}
+		dp[curNum]++
+	}
+	totalCount := 0
+	for _, count := range dp {
+		totalCount += count
+	}
+	return totalCount % mod
+}
+```