回文树/回文自动机

Author: Dev-XYS

Palindromic-Tree.cpp

@@ -0,0 +1,85 @@
+// Problem Name: Palindromes
+// Source: [APIO2014]
+
+#include <cstdio>
+#include <cstring>
+
+#define NIL 0
+#define ALPHABET_SIZE 26
+#define STRING_LENGTH 100000
+
+using namespace std;
+
+struct node
+{
+	node *next[ALPHABET_SIZE], *fail;
+	int start, len;
+	node (int _start = 0, int _len = 0) : fail(NIL), start(_start), len(_len) { memset(next, 0, sizeof(next)); }
+}*root, *empty, *last;
+
+char str[STRING_LENGTH];
+int len;
+
+void extend(char x, int pos)
+{
+	node *u = last;
+	while (str[pos] != str[pos - u->len - 1]) u = u->fail;
+	if (u->next[x] == NIL)
+	{
+		node *cur = new node(pos - u->len - 1, u->len + 2);
+		u->next[x] = cur;
+		u = u->fail;
+		if (u == NIL) cur->fail = empty;
+		else
+		{
+			while (str[pos] != str[pos - u->len - 1]) u = u->fail;
+			cur->fail = u->next[x];
+		}
+		last = cur;
+	}
+	else last = u->next[x];
+}
+
+void build()
+{
+	str[0] = '\xFF';
+	root = new node(0, -1);
+	empty = new node(0, 0);
+	empty->fail = root;
+	last = empty;
+	for (int i = 1; i <= len; i++)
+	{
+		extend(str[i] - 'a', i);
+	}
+}
+
+void print_substring(int l, int r)
+{
+	printf("\t");
+	for (int i = l; i <= r; i++)
+	{
+		printf("%c", str[i]);
+	}
+	printf("\n");
+}
+
+void dfs(node *u)
+{
+	if (u->len > 0) print_substring(u->start, u->start + u->len - 1);
+	for (int i = 0; i < ALPHABET_SIZE; i++)
+	{
+		if (u->next[i] != NIL) dfs(u->next[i]);
+	}
+}
+
+int main()
+{
+	scanf("%s", str + 1);
+	len = strlen(str + 1);
+	build();
+	printf("odd:\n");
+	dfs(root);
+	printf("even:\n");
+	dfs(empty);
+	return 0;
+}