feat: update solutions to lc problem: No.3327 (#3659)

No.3327.Check if DFS Strings Are Palindromes

Author: yanglbme

solution/3300-3399/3327.Check if DFS Strings Are Palindromes/README.md

@@ -95,32 +95,260 @@ edit_url: https://github.com/doocs/leetcode/edit/main/solution/3300-3399/3327.Ch
 
 <!-- solution:start -->
 
-### 方法一
+### 方法一：DFS + 字符串哈希
+
+我们可以使用深度优先搜索（DFS）来遍历树，将整棵树的 $\textit{dfsStr}$ 求出来，顺便求出每个节点的区间 $[l, r]$。
+
+然后我们使用字符串哈希的方法，分别求出 $\textit{dfsStr}$ 和 $\textit{dfsStr}$ 的逆序串的哈希值，判断是否是回文串。
+
+时间复杂度 $O(n)$，空间复杂度 $O(n)$。其中 $n$ 为字符串 $s$ 的长度。
 
 <!-- tabs:start -->
 
 #### Python3
 
 ```python
-
+class Hashing:
+    __slots__ = ["mod", "h", "p"]
+
+    def __init__(self, s: List[str], base: int, mod: int):
+        self.mod = mod
+        self.h = [0] * (len(s) + 1)
+        self.p = [1] * (len(s) + 1)
+        for i in range(1, len(s) + 1):
+            self.h[i] = (self.h[i - 1] * base + ord(s[i - 1])) % mod
+            self.p[i] = (self.p[i - 1] * base) % mod
+
+    def query(self, l: int, r: int) -> int:
+        return (self.h[r] - self.h[l - 1] * self.p[r - l + 1]) % self.mod
+
+
+class Solution:
+    def findAnswer(self, parent: List[int], s: str) -> List[bool]:
+        def dfs(i: int):
+            l = len(dfsStr) + 1
+            for j in g[i]:
+                dfs(j)
+            dfsStr.append(s[i])
+            r = len(dfsStr)
+            pos[i] = (l, r)
+
+        n = len(s)
+        g = [[] for _ in range(n)]
+        for i in range(1, n):
+            g[parent[i]].append(i)
+        dfsStr = []
+        pos = {}
+        dfs(0)
+
+        base, mod = 13331, 998244353
+        h1 = Hashing(dfsStr, base, mod)
+        h2 = Hashing(dfsStr[::-1], base, mod)
+        ans = []
+        for i in range(n):
+            l, r = pos[i]
+            k = r - l + 1
+            v1 = h1.query(l, l + k // 2 - 1)
+            v2 = h2.query(n - r + 1, n - r + 1 + k // 2 - 1)
+            ans.append(v1 == v2)
+        return ans
 ```
 
 #### Java
 
 ```java
-
+class Hashing {
+    private final long[] p;
+    private final long[] h;
+    private final long mod;
+
+    public Hashing(String word, long base, int mod) {
+        int n = word.length();
+        p = new long[n + 1];
+        h = new long[n + 1];
+        p[0] = 1;
+        this.mod = mod;
+        for (int i = 1; i <= n; i++) {
+            p[i] = p[i - 1] * base % mod;
+            h[i] = (h[i - 1] * base + word.charAt(i - 1)) % mod;
+        }
+    }
+
+    public long query(int l, int r) {
+        return (h[r] - h[l - 1] * p[r - l + 1] % mod + mod) % mod;
+    }
+}
+
+class Solution {
+    private char[] s;
+    private int[][] pos;
+    private List<Integer>[] g;
+    private StringBuilder dfsStr = new StringBuilder();
+
+    public boolean[] findAnswer(int[] parent, String s) {
+        this.s = s.toCharArray();
+        int n = s.length();
+        g = new List[n];
+        pos = new int[n][0];
+        Arrays.setAll(g, k -> new ArrayList<>());
+        for (int i = 1; i < n; ++i) {
+            g[parent[i]].add(i);
+        }
+        dfs(0);
+        final int base = 13331;
+        final int mod = 998244353;
+        Hashing h1 = new Hashing(dfsStr.toString(), base, mod);
+        Hashing h2 = new Hashing(new StringBuilder(dfsStr).reverse().toString(), base, mod);
+        boolean[] ans = new boolean[n];
+        for (int i = 0; i < n; ++i) {
+            int l = pos[i][0], r = pos[i][1];
+            int k = r - l + 1;
+            long v1 = h1.query(l, l + k / 2 - 1);
+            long v2 = h2.query(n + 1 - r, n + 1 - r + k / 2 - 1);
+            ans[i] = v1 == v2;
+        }
+        return ans;
+    }
+
+    private void dfs(int i) {
+        int l = dfsStr.length() + 1;
+        for (int j : g[i]) {
+            dfs(j);
+        }
+        dfsStr.append(s[i]);
+        int r = dfsStr.length();
+        pos[i] = new int[]{l, r};
+    }
+}
 ```
 
 #### C++
 
 ```cpp
-
+class Hashing {
+private:
+    vector<long long> p;
+    vector<long long> h;
+    long long mod;
+
+public:
+    Hashing(string word, long long base, int mod) {
+        int n = word.size();
+        p.resize(n + 1);
+        h.resize(n + 1);
+        p[0] = 1;
+        this->mod = mod;
+        for (int i = 1; i <= n; i++) {
+            p[i] = (p[i - 1] * base) % mod;
+            h[i] = (h[i - 1] * base + word[i - 1] - 'a') % mod;
+        }
+    }
+
+    long long query(int l, int r) {
+        return (h[r] - h[l - 1] * p[r - l + 1] % mod + mod) % mod;
+    }
+};
+
+class Solution {
+public:
+    vector<bool> findAnswer(vector<int>& parent, string s) {
+        int n = s.size();
+        vector<int> g[n];
+        for (int i = 1; i < n; ++i) {
+            g[parent[i]].push_back(i);
+        }
+        string dfsStr;
+        vector<pair<int, int>> pos(n);
+        auto dfs = [&](auto&& dfs, int i) -> void {
+            int l = dfsStr.size() + 1;
+            for (int j : g[i]) {
+                dfs(dfs, j);
+            }
+            dfsStr.push_back(s[i]);
+            int r = dfsStr.size();
+            pos[i] = {l, r};
+        };
+        dfs(dfs, 0);
+
+        const int base = 13331;
+        const int mod = 998244353;
+        Hashing h1(dfsStr, base, mod);
+        reverse(dfsStr.begin(), dfsStr.end());
+        Hashing h2(dfsStr, base, mod);
+        vector<bool> ans(n);
+        for (int i = 0; i < n; ++i) {
+            auto [l, r] = pos[i];
+            int k = r - l + 1;
+            long long v1 = h1.query(l, l + k / 2 - 1);
+            long long v2 = h2.query(n - r + 1, n - r + 1 + k / 2 - 1);
+            ans[i] = v1 == v2;
+        }
+        return ans;
+    }
+};
 ```
 
 #### Go
 
 ```go
-
+type Hashing struct {
+	p   []int64
+	h   []int64
+	mod int64
+}
+
+func NewHashing(word string, base, mod int64) *Hashing {
+	n := len(word)
+	p := make([]int64, n+1)
+	h := make([]int64, n+1)
+	p[0] = 1
+	for i := 1; i <= n; i++ {
+		p[i] = p[i-1] * base % mod
+		h[i] = (h[i-1]*base + int64(word[i-1])) % mod
+	}
+	return &Hashing{p, h, mod}
+}
+
+func (hs *Hashing) query(l, r int) int64 {
+	return (hs.h[r] - hs.h[l-1]*hs.p[r-l+1]%hs.mod + hs.mod) % hs.mod
+}
+
+func findAnswer(parent []int, s string) (ans []bool) {
+	n := len(s)
+	g := make([][]int, n)
+	for i := 1; i < n; i++ {
+		g[parent[i]] = append(g[parent[i]], i)
+	}
+	dfsStr := []byte{}
+	pos := make([][2]int, n)
+	var dfs func(int)
+	dfs = func(i int) {
+		l := len(dfsStr) + 1
+		for _, j := range g[i] {
+			dfs(j)
+		}
+		dfsStr = append(dfsStr, s[i])
+		r := len(dfsStr)
+		pos[i] = [2]int{l, r}
+	}
+
+	const base = 13331
+	const mod = 998244353
+	dfs(0)
+	h1 := NewHashing(string(dfsStr), base, mod)
+	for i, j := 0, len(dfsStr)-1; i < j; i, j = i+1, j-1 {
+		dfsStr[i], dfsStr[j] = dfsStr[j], dfsStr[i]
+	}
+	h2 := NewHashing(string(dfsStr), base, mod)
+	for i := 0; i < n; i++ {
+		l, r := pos[i][0], pos[i][1]
+		k := r - l + 1
+		v1 := h1.query(l, l+k/2-1)
+		v2 := h2.query(n-r+1, n-r+1+k/2-1)
+		ans = append(ans, v1 == v2)
+	}
+	return
+}
 ```
 
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