P9623 [ICPC 2020 Nanjing R] Baby's First Suffix Array Problem

A suffix array for string $s$ of length $n$ is a permutation $sa$ of integers from $1$ to $n$ such that $s[sa_1.. n], s[sa_2..n], \dots, s[sa_n..n]$ is the list of non-empty suffixes of $s$ sorted in lexicographical order. The rank table for suffixex of $s$ is a permutation $rank$ of integers from $1$ to $n$ such that $rank_{sa_i} = i$. Kotori has a string $s=s_1s_2\dots s_n$. She would like to ask $m$ queries. And in the $i$-th query, a substring $x=s[l_i..r_i]$ of $s$ is given, Kotori would like to know the rank of suffix $s[k_i..r_i]$ of $x$. Note $s[l..r]$ means the substring of $s$ which starts from the $l$-th position and ends at the $r$-th position, both inclusive.

There are multiple test cases. The first line of the input contains an integer $T$ indicating the number of test cases. For each test case: The first line contains two integers $n$ and $m$ ($1 \le n, m \le 5 \times 10^4$) -- the length of the string and the number of queries. The second line contains a string $s$ of length $n$ consisting only of lowercase English letters. Each of the next $m$ lines contains three integers $l_i$, $r_i$ and $k_i$ ($1 \le l_i \le r_i \le n, l_i \le k_i \le r_i$) denoting a query. It is guaranteed that neither the sum of $n$ or the sum of $m$ of all test cases will exceed $5 \times 10^4$.

For each query output one line containing one integer denoting the answer.