1110. Delete Nodes And Return Forest

use a param to indicate if it will be a root

1122. Relative Sort Array

sort

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use a sort len of 1001 to store counts in arr1, loop arr2 to place to target arr, then result of the numbers in arr to target arr

1143. Longest Common Subsequence

memoized recursion / dp

1175. Prime Arrangements

先筛出范围内有多少个素数，再利用全排列公式得到结果 primes_c! * (n - primes_c)!