problem1 link 令$f[x1][y1][x2][y2]$表示矩形(x1,y1)(x2,y2)中能选出的最大值.dp即可. problem2 link 这个题应该有更好的递推公式. 我的做法是这样的.设$f[i]$表示$i$时的答案,令$g[i]=f[i]-f[i-1]$.通过暴力计算$g$的前几项,发现$g$的公式为 $g(n+2)=a(n)=\frac{(2n+3)*(6n^4+36n^3+76n^2+66n+5)}{960}-\frac{(-1)^n}{64}$ problem3…
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…
