Lawnmower
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
You have a garden consisting entirely of grass and weeds. Your garden is described by an n × m grid, with rows numbered 1 to n from top to bottom, and columns 1 to m from left to right. Each cell is identified by a pair (r, c) which means that the cell is located at row r and column c. Each cell may contain either grass or weeds. For example, a 4 × 5 garden may look as follows (empty cells denote grass):
You have a land-mower with you to mow all the weeds. Initially, you are standing with your lawnmower at the top-left corner of the garden. That is, at cell (1, 1). At any moment of time you are facing a certain direction — either left or right. And initially, you face right.
In one move you can do either one of these:
- Move one cell in the direction that you are facing.
-
if you are facing right: move from cell
(r, c)
to cell
(r, c + 1)
-
if you are facing left: move from cell
(r, c)
to cell
(r, c - 1)
- Move one cell down (that is, from cell
(r, c)
to cell
(r + 1, c)
), and change your direction to the opposite one.
-
if you were facing right previously, you will face left
-
if you were facing left previously, you will face right
You are not allowed to leave the garden. Weeds will be mowed if you and your lawnmower are standing at the cell containing the weeds (your direction doesn’t matter). This action isn’t counted as a move.
What is the minimum number of moves required to mow all the weeds?
Input
The first line contains two integers n and m (1 ≤ n, m ≤ 150) — the number of rows and columns respectively. Then follow n lines containing m characters each — the content of the grid. “G” means that this cell contains grass. “W” means that this cell contains weeds.
It is guaranteed that the top-left corner of the grid will contain grass.
Output
Print a single number — the minimum number of moves required to mow all the weeds.
Examples
input
Copy
4 5
GWGGW
GGWGG
GWGGG
WGGGG
output
Copy
11
input
Copy
3 3
GWW
WWW
WWG
output
Copy
7
input
Copy
1 1
G
output
Copy
0
Note
For the first example, this is the picture of the initial state of the grid:
A possible solution is by mowing the weeds as illustrated below:
题目大意
一个人割草，输入一个
的图，G代表空地，W代表草，奇数行只能往右走，偶数行只能往左走。问割完草的最少步数。
题目分析
之前各种想，各种特殊情况处理特判……其实只要知道一个矩形图，一个角走到另一个角，只要不往回走，其实走的路径就是一样的。不用考虑一定是往那条路走。那么只要模拟一下走的过程，记录一下步数就行了。我们从左上角走，然后往右遍历找到就计算一下距离，更新一下当前的位置，然后第二行从右往左扫。第三行从左往右扫，如此循环即可。
代码
#include <cstdio>
#include <cmath>
#include <algorithm>
using namespace std;
typedef struct{
int x, y;
}node;
typedef long long ll;
const int inf = 0x3f3f3f3f;
int n, m, x, y, k;
ll f(node v){
int a = inf, b = inf;
if(v.x < 0)
a = (x - 1) / abs(v.x);
else if(v.x > 0)
a = (n - x) / abs(v.x);
if(v.y < 0)
b = (y - 1) / abs(v.y);
else if(v.y > 0)
b = (m - y) / abs(v.y);
int mn = min(a, b);
x += mn * v.x; y += mn * v.y;
return mn;
}
int main(int argc, char const *argv[]) {
scanf("%d%d%d%d", &n, &m, &x, &y);
scanf("%d", &k);
ll ans = 0;
for(int i = 0; i < k; i++){
node t;
scanf("%d%d", &t.x, &t.y);
ans += f(t);
}
printf("%I64d\n", ans);
return 0;
}