7640: [CSES Problem Set] Required Substring
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Description
Your task is to calculate the number of strings of length nn having a given pattern of length $m$ as their substring. All strings consist of characters A–Z.
Input
The first input line has an integer $n$: the length of the final string.
The second line has a pattern of length $m$.
The second line has a pattern of length $m$.
Output
Print the number of strings modulo $10^9+7$.
Constraints
$1≤n≤1000$
$1 \le m \le 100$
$1 \le m \le 100$
Sample 1 Input
6
ABCDB
Sample 1 Output
52
The final string will be of the form ABCDB$x$ or $x$ABCDB where $x$ is any character between A–Z.