problem1 link 从前向后确定一下,然后再从后向前确定一下.一样的话就是可以确定的. problem2 link 首先将强连通分量缩点.理论上来说,只需要遍历所有入度为0的联通块中的一个即可. 但是有一种情况可能是某个入度为0的联通块只包含一个节点$u$,这时当遍历完其他入度为0的联通块时即可确定节点$u$. problem3 link 当$N$不能整除$H$时无解. 设连续的电梯长度为$L$.那么两个相邻的连续电梯块之间的长度也一定是$L$的倍数. 设$f(H,N)$表示$L>1$的…
problem1 link 倒着想.每次添加一个右括号再添加一个左括号,直到还原.那么每次的右括号的选择范围为当前左括号后面的右括号减去后面已经使用的右括号. problem2 link 令$h(x)=\sum_{i=1}^{x}g(i)$,那么答案为$h(R)-h(L-1)$.对于$h(x)$: (1)如果$x\leq K$,那么$h(x)=0$ (2)否则对于$[K+1,x]$之间的所有偶数来说,对答案的贡献为$even+h(\frac{x}{2})-h(\frac{K}{2})$,其中$e…
Problem Statement You are given the ints perimeter and area. Your task is to find a triangle with the following properties: The coordinates of each vertex are integers between 0 and 3000, inclusive. The perimeter of the triangle must be exactly…
Problem Statement The Happy Letter game is played as follows: At the beginning, several players enter the field. Each player has a lowercase English letter on their back. The game is played in turns. In each turn, you select two players with dif…
