POJ 2406 Power Strings(next数组应用)
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G - Power Strings
Time Limit:3000MS Memory Limit:65536KB 64bit IO Format:%lld & %lluDescription
Given two strings a and b we define a*b to be their concatenation. For example, if a = "abc" and b = "def" then a*b = "abcdef". If we think of concatenation as multiplication, exponentiation by a non-negative integer is defined in the normal way: a^0 = "" (the empty string) and a^(n+1) = a*(a^n).
Input
Each test case is a line of input representing s, a string of printable characters. The length of s will be at least 1 and will not exceed 1 million characters. A line containing a period follows the last test case.
Output
For each s you should print the largest n such that s = a^n for some string a.
Sample Input
abcdaaaaababab.
Sample Output
143
Hint
This problem has huge input, use scanf instead of cin to avoid time limit exceed.
题意:给你一个字符串,让你求这个字符串是由多少个相同的子串构成的,要求子串数量尽量多;
思路:如果你随便找一个循环构成的子串,对他手动构造kmp的next数组,你会发现,出了第一个周期,其余的周期next数组都是增加的,而且这个周期肯定是最短周期
假如由k个周期,next[n]肯定就是k-1个周期的字母个数,用n - next[n]就求出第一个周期的长度,如果能用总长度n对n - next[n]正好取膜,说明他是第一个周期。。
如果不能整除,可能是这个循环子串前面加了一些东西,或者就只有一个。。
#include <iostream>#include <cstdio>#include <cstring>using namespace std;const int maxn = 1e6 + 5;int next[maxn];char str[maxn];int compute(int *next, char *p){ int l = strlen(p); int k = 0; next[0] = next[1] = 0; for(int i = 2; i <= l; i++) { while(k && p[k] != p[i-1]) k = next[k]; if(p[k] == p[i-1]) k++; next[i] = k; } return l-next[l];}int main(){ while(~scanf("%s",str) && strcmp(str,".")) { int n = strlen(str); int k = compute(next,str); if(n%k == 0) cout << n/k << endl; else cout << 1 << endl; } return 0;}
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