Alice and Bob love playing one-dimensional battle ships. They play on the field in the form of a line consisting of n square cells (that is, on a 1 × n table).
At the beginning of the game Alice puts k ships on the field without telling their positions to Bob. Each ship looks as a 1 × a rectangle (that is, it occupies a sequence of a consecutive squares of the field). The ships cannot intersect and even touch each other.
After that Bob makes a sequence of "shots". He names cells of the field and Alice either says that the cell is empty ("miss"), or that the cell belongs to some ship ("hit").
But here's the problem! Alice like to cheat. May be that is why she responds to each Bob's move with a "miss".
Help Bob catch Alice cheating — find Bob's first move, such that after it you can be sure that Alice cheated.
The first line of the input contains three integers: n, k and a (1 ≤ n, k, a ≤ 2·105) — the size of the field, the number of the ships and the size of each ship. It is guaranteed that the n, k and a are such that you can put k ships of size a on the field, so that no two ships intersect or touch each other.
The second line contains integer m (1 ≤ m ≤ n) — the number of Bob's moves.
The third line contains m distinct integers x1, x2, ..., xm, where xi is the number of the cell where Bob made the i-th shot. The cells are numbered from left to right from 1 to n.
Print a single integer — the number of such Bob's first move, after which you can be sure that Alice lied. Bob's moves are numbered from 1 to m in the order the were made. If the sought move doesn't exist, then print "-1".
11 3 3 5 4 8 6 1 11
3
5 1 3 2 1 5
-1
5 1 3 1 3
1
题目大意：Alice和Bob玩游戏。Alice在一段长度为n的线段上放了k只战舰，战舰不能重叠，每只战舰的长度都是a（即要占去a个连续的整点）。Bob可以射击m次每次射击一个整数点，Alice会告诉他是否击中。然而Alice作弊，无论为没有打中，她都说没打中。求在Bob第几次射击后可以确定Alice作弊了。
一段连续的线段上能放的战舰数量为（左端点-右端点+2）/（a+1）。每次射击就相当于把被射击的点所在的线段分成两段，如果在某次射击后所有线段能容纳的战舰数小于k，就能确定Alice作弊。可以用set维护这些线段。
代码在此。
评论 (0)
