POJ 1200 Crazy Search(RK)

题意

给定一个由NC个字母组成的字符串，求长度为N的不同子串的个数

思路：

由于只有NC个字母，可以将字母编号，0 ～ NC - 1，转换成数字，就可以将字符串表示成NC进制的数字，这样所有字串代表的数字都是唯一的，转换成10进制的数也是唯一的！

就像10的二进制表示只有1010

例如

3 4
daababac

d = 3

a = 0

b = 1

c = 2

daa = 3 * 4 ^ 2 + 0 * 4 ^ 1 + 0 * 4 ^ 0 = 48

//vs1.0
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX 16000000

char str[MAX];
bool hash[MAX];
int ancii[128];

int main() {
int N, NC;
while (scanf("%d%d%s", &N, &NC, str) != EOF) {
memset(hash, true, sizeof(hash));
memset(ancii, 0, sizeof(ancii));
int cnt = 0;
for (char *s=str; *s; ++s) {
if (!ancii[*s]) {
ancii[*s] = ++cnt;
if (NC == cnt) break;
}
}
int sum;
int ans = 0;
int len = strlen(str) - N + 1;
for (int i=0; i<len; ++i) {
sum = 0;
for (int j=0; j<N; ++j) sum = sum * NC + (ancii[str[i+j]] - 1);
if (hash[sum]) {
++ans;
hash[sum] = false;
}
}
printf ("%d\n", ans);
}
return 0;
}

//vs2.0
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX 16000000

char str[MAX];
bool hash[MAX];
int ancii[128];

int main() {
int N, NC;
while (scanf("%d%d%s", &N, &NC, str) != EOF) {
memset(hash, true, sizeof(hash));
memset(ancii, 0, sizeof(ancii));
int cnt = 0;
for (char *s=str; *s; ++s) {
if (!ancii[*s]) {
ancii[*s] = ++cnt;
if (NC == cnt) break;
}
}
int sum = 0;
int tmp = 1;
for (int i=0; i<N; ++i) {
tmp *= NC;
sum = sum * NC + ancii[str[i]] - 1;
}
tmp /= NC;
hash[sum] = false;
int ans = 1;
int len = strlen(str);
for (int i=N; i<len; ++i) {
sum = (sum - tmp * (ancii[str[i-N]]-1)) * NC + ancii[str[i]] - 1;
if (hash[sum]) {
++ans;
hash[sum] = false;
}
}
printf ("%d\n", ans);
}
return 0;
}