feat: add solutions to lc problem: No.3291 (#3530)

No.3291.Minimum Number of Valid Strings to Form Target I

Author: yanglbme

solution/3200-3299/3291.Minimum Number of Valid Strings to Form Target I/README.md

@@ -84,32 +84,281 @@ edit_url: https://github.com/doocs/leetcode/edit/main/solution/3200-3299/3291.Mi
 
 <!-- solution:start -->
 
-### 方法一
+### 方法一：字典树 + 记忆化搜索
+
+我们可以使用字典树存储所有有效字符串，然后使用记忆化搜索计算答案。
+
+我们设计一个函数 $\textit{dfs}(i)$，表示从字符串 $\textit{target}$ 的第 $i$ 个字符开始，需要连接的最少字符串数量。那么答案就是 $\textit{dfs}(0)$。
+
+函数 $\textit{dfs}(i)$ 的计算方式如下：
+
+-   如果 $i \geq n$，表示字符串 $\textit{target}$ 已经遍历完了，返回 $0$；
+-   否则，我们可以从字典树中找到以 $\textit{target}[i]$ 开头的有效字符串，然后递归计算 $\textit{dfs}(i + \text{len}(w))$，其中 $w$ 是找到的有效字符串。我们取这些值中的最小值加 $1$ 作为 $\textit{dfs}(i)$ 的返回值。
+
+为了避免重复计算，我们使用记忆化搜索。
+
+时间复杂度 $O(n^2 + L)$，空间复杂度 $O(n + L)$。其中 $n$ 是字符串 $\textit{target}$ 的长度，而 $L$ 是所有有效字符串的总长度。
 
 <!-- tabs:start -->
 
 #### Python3
 
 ```python
-
+def min(a: int, b: int) -> int:
+    return a if a < b else b
+
+
+class Trie:
+    def __init__(self):
+        self.children: List[Optional[Trie]] = [None] * 26
+
+    def insert(self, w: str):
+        node = self
+        for i in map(lambda c: ord(c) - 97, w):
+            if node.children[i] is None:
+                node.children[i] = Trie()
+            node = node.children[i]
+
+
+class Solution:
+    def minValidStrings(self, words: List[str], target: str) -> int:
+        @cache
+        def dfs(i: int) -> int:
+            if i >= n:
+                return 0
+            node = trie
+            ans = inf
+            for j in range(i, n):
+                k = ord(target[j]) - 97
+                if node.children[k] is None:
+                    break
+                node = node.children[k]
+                ans = min(ans, 1 + dfs(j + 1))
+            return ans
+
+        trie = Trie()
+        for w in words:
+            trie.insert(w)
+        n = len(target)
+        ans = dfs(0)
+        return ans if ans < inf else -1
 ```
 
 #### Java
 
 ```java
-
+class Trie {
+    Trie[] children = new Trie[26];
+
+    void insert(String w) {
+        Trie node = this;
+        for (int i = 0; i < w.length(); ++i) {
+            int j = w.charAt(i) - 'a';
+            if (node.children[j] == null) {
+                node.children[j] = new Trie();
+            }
+            node = node.children[j];
+        }
+    }
+}
+
+class Solution {
+    private Integer[] f;
+    private char[] s;
+    private Trie trie;
+    private final int inf = 1 << 30;
+
+    public int minValidStrings(String[] words, String target) {
+        trie = new Trie();
+        for (String w : words) {
+            trie.insert(w);
+        }
+        s = target.toCharArray();
+        f = new Integer[s.length];
+        int ans = dfs(0);
+        return ans < inf ? ans : -1;
+    }
+
+    private int dfs(int i) {
+        if (i >= s.length) {
+            return 0;
+        }
+        if (f[i] != null) {
+            return f[i];
+        }
+        Trie node = trie;
+        f[i] = inf;
+        for (int j = i; j < s.length; ++j) {
+            int k = s[j] - 'a';
+            if (node.children[k] == null) {
+                break;
+            }
+            f[i] = Math.min(f[i], 1 + dfs(j + 1));
+            node = node.children[k];
+        }
+        return f[i];
+    }
+}
 ```
 
 #### C++
 
 ```cpp
-
+class Trie {
+public:
+    Trie* children[26]{};
+
+    void insert(string& word) {
+        Trie* node = this;
+        for (char& c : word) {
+            int i = c - 'a';
+            if (!node->children[i]) {
+                node->children[i] = new Trie();
+            }
+            node = node->children[i];
+        }
+    }
+};
+
+class Solution {
+public:
+    int minValidStrings(vector<string>& words, string target) {
+        int n = target.size();
+        Trie* trie = new Trie();
+        for (auto& w : words) {
+            trie->insert(w);
+        }
+        const int inf = 1 << 30;
+        int f[n];
+        memset(f, -1, sizeof(f));
+        auto dfs = [&](auto&& dfs, int i) -> int {
+            if (i >= n) {
+                return 0;
+            }
+            if (f[i] != -1) {
+                return f[i];
+            }
+            f[i] = inf;
+            Trie* node = trie;
+            for (int j = i; j < n; ++j) {
+                int k = target[j] - 'a';
+                if (!node->children[k]) {
+                    break;
+                }
+                node = node->children[k];
+                f[i] = min(f[i], 1 + dfs(dfs, j + 1));
+            }
+            return f[i];
+        };
+        int ans = dfs(dfs, 0);
+        return ans < inf ? ans : -1;
+    }
+};
 ```
 
 #### Go
 
 ```go
+type Trie struct {
+	children [26]*Trie
+}
+
+func (t *Trie) insert(word string) {
+	node := t
+	for _, c := range word {
+		idx := c - 'a'
+		if node.children[idx] == nil {
+			node.children[idx] = &Trie{}
+		}
+		node = node.children[idx]
+	}
+}
+
+func minValidStrings(words []string, target string) int {
+	n := len(target)
+	trie := &Trie{}
+	for _, w := range words {
+		trie.insert(w)
+	}
+	const inf int = 1 << 30
+	f := make([]int, n)
+	var dfs func(int) int
+	dfs = func(i int) int {
+		if i >= n {
+			return 0
+		}
+		if f[i] != 0 {
+			return f[i]
+		}
+		node := trie
+		f[i] = inf
+		for j := i; j < n; j++ {
+			k := int(target[j] - 'a')
+			if node.children[k] == nil {
+				break
+			}
+			f[i] = min(f[i], 1+dfs(j+1))
+			node = node.children[k]
+		}
+		return f[i]
+	}
+	if ans := dfs(0); ans < inf {
+		return ans
+	}
+	return -1
+}
+```
 
+#### TypeScript
+
+```ts
+class Trie {
+    children: (Trie | null)[] = Array(26).fill(null);
+
+    insert(word: string): void {
+        let node: Trie = this;
+        for (const c of word) {
+            const i = c.charCodeAt(0) - 'a'.charCodeAt(0);
+            if (!node.children[i]) {
+                node.children[i] = new Trie();
+            }
+            node = node.children[i];
+        }
+    }
+}
+
+function minValidStrings(words: string[], target: string): number {
+    const n = target.length;
+    const trie = new Trie();
+    for (const w of words) {
+        trie.insert(w);
+    }
+    const inf = 1 << 30;
+    const f = Array(n).fill(0);
+
+    const dfs = (i: number): number => {
+        if (i >= n) {
+            return 0;
+        }
+        if (f[i]) {
+            return f[i];
+        }
+        f[i] = inf;
+        let node: Trie | null = trie;
+        for (let j = i; j < n; ++j) {
+            const k = target[j].charCodeAt(0) - 'a'.charCodeAt(0);
+            if (!node?.children[k]) {
+                break;
+            }
+            node = node.children[k];
+            f[i] = Math.min(f[i], 1 + dfs(j + 1));
+        }
+        return f[i];
+    };
+
+    const ans = dfs(0);
+    return ans < inf ? ans : -1;
+}
 ```
 
 <!-- tabs:end -->