Codeforces 432D Prefixes and Suffixes(KMP+dp)

题目连接：Codeforces 432D Prefixes and Suffixes

题目大意：给出一个字符串，求所有既是前缀串又是后缀串的字符串出现了几次。

解题思路：根据性质可以根据KMP算法求出所有的前后缀串，然后利用dp求解，dp[i]表示从1到i这个子串出现过的次数。转移方程dp[jump[i]]+=dp[i]。任意一个dp[i]的初始状态应该是1。

#include <cstdio>
#include <cstring>

const int N = 1e5+5;

int n, jump
, c, r
, dp
;
char str
;

void getJump() {
int k = 0;
n = strlen(str+1);
for (int i = 2; i <= n; i++) {
while (k && str[i] != str[k+1])
k = jump[k];

if (str[i] == str[k+1])
k++;
jump[i] = k;
}
}

int main () {
scanf("%s", str+1);
getJump();

c = 0;
for (int i = jump
; i; i = jump[i]) {
r[c] = i;
c++;
}

memset(dp, 0, sizeof(dp));
for (int i = n; i; i--) {
dp[i]++;
dp[jump[i]] += dp[i];
}

printf("%d\n", c+1);
for (int i = c-1; i >= 0; i--)
printf("%d %d\n", r[i], dp[r[i]]);
printf("%d %d\n", n, dp
);
return 0;
}