Just another archive of solutions to some interesting DSA problems.

Counting Arrays:

There is an array of n non-negative integers, arr. In one operation, some positive integer x is chosen and 1 subtracted from all the numbers of the array which are greater than or equal to x. Find the number of different final arrays possible after the operation is applied 0 or more times. Return the answer modulo (10^9 + 7).

Note:

• Different values of x can be chosen for different operations.
• Two final arrays a and b are considered different if there is at least one index i such that a[i] != b[i]

Constraints:

• 1 <= n <= 10^5
• 0 <= arr[i] <= 10^5