Canadian Computing Competition: 2020 Stage 1, Senior #4
There are ~N~ people sitting at a circular table for a long session of negotiations. Each person belongs to one of the three groups:
C. A group is happy if all of its members are sitting contiguously in a block of consecutive seats. You would like to make all groups happy by some sequence of swap operations. In each swap operation, two people exchange seats with each other. What is the minimum number of swaps required to make all groups happy?
The input consists of a single line containing ~N~ ~(1 \le N \le 1\,000\,000)~ characters, where each character is
C. The ~i~-th character denotes the group of the person initially sitting at the ~i~-th seat at the table, where seats are numbered in clockwise order.
For ~4~ of the ~15~ available marks, the input has no ~C~ characters and ~N \le 5\,000~.
For an additional ~4~ of the ~15~ available marks, the input has no ~C~ characters.
For an additional ~4~ of the ~15~ available marks, ~N \le 5\,000~.
Output a single integer, the minimum possible number of swaps.
Output for Sample Input
Explanation of Output for Sample Input
In one possible sequence, the first swap results in the seating layout
AABCBCBCCA. After the second swap, the layout is