A. CQXYM Count Permutations Solution: It is not difficult to think that there are x of i satisfying the condition in an permutations , then if we reverse the permutations, there are 2n-x of i satisfying the condition.…
Solution: First of all, we can almost immediately notice that if x[i]>m, then this must have no effect, and we can ignore it directly. Therefore, the value range of x[i] is reduced from 0~$10^9$ to 0~$2\cdot 10^5$.…
Solution: First of all, we do not consider the condition that the number of good numbers is exactly equal to k, we first consider the characteristics of the good number itself.…
Solution: It is not difficult to find that when a=5 and b=4, only 16 steps are required even in the worst case.…
A. Casimir's String Solitaire Solution: Obviously, Yes if and only if the sum of the number of letter A and letter C is equal to the number of letter B, otherwise No.…
Solution: First of all, let's think about the simplest way: Obviously, for every segment, there will be two possibilities of going to the left or right. Each possibility contains three pieces of information:…
A. Regular Bracket Sequences Solution: Taking n=5 as an example, we can write 1 solution at once: ()()()()(). Then we can write the following 4 solutions:(())()()()()()(())()()()()()(())()()()()()()(())…
A. Countdown Solution: Obviously, we will replace every non-zero number with the ones digit and then subtract it.Therefore, in addition to the operation required for this number to be subtracted, a swap operation can be added. (Except for the ones digit itself)…
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