[洛谷P4656][CEOI2017]Palindromic Partitions

题目大意：一个长度为$n$的字符串，要求把它分成尽可能多的小块，使得这些块构成回文串

题解：贪心，从两边从找尽可能小的块使得左右的块相等，判断相等可以用$hash$

卡点：无

C++ Code：

#include <cstdio>
#include <cstring>
#define maxn 1000010
const long long base = 233, mod = 1000000007;
int Tim;
int n, mid;
long long pw[maxn], hsh[maxn];
char s[maxn];
inline long long ghsh(int l, int r) {
	return ((hsh[r] - hsh[l - 1] * pw[r - l + 1]) % mod + mod) % mod;
}
inline bool check(int l, int r, int len) {
	return ghsh(l, l + len - 1) == ghsh(r, r + len - 1);
}
int work(int l, int r) {
	if (l > r) return 0;
	if (l == r) return 1;
	int len;
	for (int i = r; i > mid; i--) {
		len = r - i + 1;
		if (check(l, i, len)) return work(l + len, i - 1) + 2;
	}
	return 1;
}
int main() {
	scanf("%d", &Tim);
	pw[0] = 1; for (int i = 1; i < maxn; i++) pw[i] = pw[i - 1] * base % mod;
	while (Tim --> 0) {
		scanf("%s", s + 1);
		n = strlen(s + 1);
		mid = n + 1 >> 1;
		for (int i = 1; i <= n; i++) hsh[i] = (hsh[i - 1] * base + s[i]) % mod;
		printf("%d
", work(1, n));
	}
	return 0;
}