HDU 4333 Revolving Digits 扩展KMP

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题目来源：HDU 4333 Revolving Digits

题意：求一个数字循环移动后有多少个不同的小于等于大于的数字

思路：扩展KMP求出S[i..j]等于S[0..j-i]的最长前缀判断 next[i] 大于等于n就是相同小于n判断S[next[i]]和S[next[i]+i]的大小

next数组的含义就是S字符串以i开始的和S本身(以0开始)的最长公共前缀把题目输入的复制一倍然后直接判断next数组比较大小就行了

#include <cstdio>#include <cstring>using namespace std;const int maxn = 200010;int f[maxn];char a[maxn];void getFail(char* s){int n = strlen(s);int p = 0, k = 1;for(int i = 0; i+1 < n && s[i] == s[i+1]; i++)p++;f[0] = n;f[1] = p;for(int i = 2; i < n/2; i++){int p = f[k]+k-1;int l = f[i-k];if(i+l-1 < p)f[i] = l;else{int j = p-i+1;if(j < 0)j = 0;while(i+j < n*2 && s[i+j] == s[j])j++;f[i] = j;k = i;}}}int main(){int cas = 1;int T;scanf("%d", &T);while(T--){scanf("%s", a);int n = strlen(a);for(int i = 0; i < n; i++){a[i+n] = a[i];}a[2*n] = 0;getFail(a);int len;for(len = 1; len <= n; len++){if(f[len]+len >= n){if(n%len)len = n;break;}}int sum1 = 0, sum2 = 0, sum3 = 0;for(int i = 0; i < len; i++){if(f[i] >= n)sum2++;else if(a[i+f[i]] > a[f[i]])sum3++;elsesum1++;}printf("Case %d: %d %d %d\n", cas++, sum1, sum2, sum3);}return 0;}

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