CodeForces - 1016B
You are given two strings ss and tt, both consisting only of lowercase Latin letters.
The substring s[l..r]s[l..r] is the string which is obtained by taking characters sl,sl+1,…,srsl,sl+1,…,sr without changing the order.
Each of the occurrences of string aa in a string bb is a position ii (1≤i≤|b|−|a|+11≤i≤|b|−|a|+1) such that b[i..i+|a|−1]=ab[i..i+|a|−1]=a (|a||a| is the length of string aa).
You are asked qq queries: for the ii-th query you are required to calculate the number of occurrences of string tt in a substring s[li..ri]s[li..ri].
Input
The first line contains three integer numbers nn, mm and qq (1≤n,m≤1031≤n,m≤103, 1≤q≤1051≤q≤105) — the length of string ss, the length of string tt and the number of queries, respectively.
The second line is a string ss (|s|=n|s|=n), consisting only of lowercase Latin letters.
The third line is a string tt (|t|=m|t|=m), consisting only of lowercase Latin letters.
Each of the next qq lines contains two integer numbers lili and riri (1≤li≤ri≤n1≤li≤ri≤n) — the arguments for the ii-th query.
Output
Print qq lines — the ii-th line should contain the answer to the ii-th query, that is the number of occurrences of string tt in a substring s[li..ri]s[li..ri].
Examples
10 3 4
codeforces
for
1 3
3 10
5 6
5 7
0
1
0
1
15 2 3
abacabadabacaba
ba
1 15
3 4
2 14
4
0
3
3 5 2
aaa
baaab
1 3
1 1
0
0
Note
In the first example the queries are substrings: "cod", "deforces", "fo" and "for", respectively.
刚开始不会做,是因为只想到了用前缀和,没想到应该怎么去用,根据题意,只有当string t 全部在在所查区间的时候,答案才加一,
所以说如果从查询区间的头部向后遍历的话,不但要知道从哪个字母开始,还要判断字符串t何时结束,前缀和不太好维护。
因此,我们从查询区间的尾部向前遍历,只要找到字符串t结束的地方,只需要判断字符串t的开头是否在查询区间之内即可,这样的前缀和容易维护。
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<string>
#include<cmath>
#include<algorithm>
#include<queue>
#include<stack>
#include<deque>
#include<map>
#include<iostream>
using namespace std;
typedef long long LL;
const double pi=acos(-1.0);
const double e=exp();
const int N = ; char con[],sub[];
int check[];
int main()
{
int i,p,j,n,m,q;
int flag,a,b,ans;
scanf("%d%d%d",&n,&m,&q);
scanf(" %s",con+);
scanf(" %s",sub+); for(i=;i<=n-m+;i++)
{
p=;
flag=;
for(j=i;j<=i+m;j++)
{
if(p>m)
{
flag=;
break;
}
if(con[j]!=sub[p])
break;
p++;
}
if(flag==)
check[j-]=;
}
for(i=;i<=q;i++)
{
ans=;
scanf("%d%d",&a,&b);
for(j=a;j<=b;j++)
{
if(check[j]==&&j-(m-)>=a)
ans++;
}
printf("%d\n",ans);
}
return ;
}
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