pku 3009 Curling 2.0 DFS+剪枝

开始用第一种方式写的,总是WA,郁闷,至今还不知为啥,希望高人指点,用第二种方式写后,AC.

if(step > 10)
return;

这样剪枝后,168k, 250ms.

再剪枝,

if(step > 10 || step >= minStep)
return;

168k 79ms.

//WA
#include <iostream>
using namespace std;

int startx, starty, endx, endy;
int w, h;
int map[22][22];
int minCount;

struct Point{
int x,y;
};

bool ok(int x, int y, Point& p, int c)
{
int i;
p.x = x, p.y = y;

if(c == 0)
{
for(i = x-1; i >= 0; i--)
if(map[y][i] == 1 || map[y][i] == 3)
break;
if(i == -1 || i == x-1&&map[y][i] == 1)
return false;
else if(map[y][i] == 3)
p.x = i;
else
p.x = i+1;
}
else if(c == 1)
{
for(i = y-1; i >= 0; i--)
if(map[i][x] == 1 || map[i][x] == 3)
break;
if(i == -1 || i == y-1&&map[i][x] == 1)
return false;
else if(map[i][x] == 3)
p.y = i;
else
p.y = i+1;
}
else if(c == 2)
{
for(i = x+1; i < w; ++i)
if(map[y][i] == 1 || map[y][i] == 3)
break;
if(i == w|| i == x+1&&map[y][i]==1)
return false;
else if(map[y][i] == 3)
p.x = i;
else
p.x = i-1;
}
else
{
for(i = y+1; i < h; ++i)
if(map[i][x] == 1 || map[i][x] == 3)
break;
if(i == h || i == y+1&&map[i][x]==1)
return false;
else if(map[i][x] == 3)
p.y = i;
else
p.y = i-1;
}
return true;
}

void dfs(int x, int y, int n)
{
if(n > 10)
return;

if(x == endx && y == endy)
{
if(n < minCount)
minCount = n;
return;
}

for(int i = 0; i < 4; ++i)
{
Point p;
if(ok(x, y, p, i))
{
//printf("newx=%d,newy=%d/n", p.x, p.y);
if(i == 0)
map[p.y][p.x-1] = 0;
else if(i == 1)
map[p.y-1][p.x] = 0;
else if(i == 2)
map[p.y][p.x+1] = 0;
else
map[p.y+1][p.x] = 0;

dfs(p.x, p.y, n+1);

if(i == 0)
map[p.y][p.x-1] = 1;
else if(i == 1)
map[p.y-1][p.x] = 1;
else if(i == 2)
map[p.y][p.x+1] = 1;
else
map[p.y+1][p.x] = 1;
}
}
}

int main()
{
//freopen("in.txt", "r", stdin);
//freopen("out.txt", "w", stdout);

while(scanf("%d%d", &w, &h) && w)
{
for (int i = 0; i < h; ++i)
for (int j = 0;j < w; ++j)
{
scanf("%d", &map[i][j]);
if(map[i][j] == 2)
startx = j, starty = i;
else if(map[i][j] == 3)
endx = j, endy = i;
}

minCount = 0x7fffffff;
dfs(startx, starty, 0);
if(minCount == 0x7fffffff || minCount > 10)
printf("-1/n");
else
printf("%d/n", minCount);
}
return 0;
}

//AC
#include <iostream>
using namespace std;

int dx[] = {-1, 0, 1, 0};
int dy[] = {0, -1, 0, 1};
int w, h;
int map[20][20];
int startx, starty;
int minStep;

enum square_t{
VACANT = 0,
BLOCK,
START,
GOAL
};

inline bool ok(int x, int y)
{
if(x < 0 || x >= w || y < 0 || y >= h)
return false;
return true;
}

void dfs(int x, int y, int step)
{
if(step > 10 || step >= minStep)
return;

for(int i = 0; i < 4; ++i)
{
int tempx = x, tempy = y;
if(!ok(tempx+dx[i], tempy+dy[i]) || map[tempy+dy[i]][tempx+dx[i]] == BLOCK)
continue;

while(true)
{
if(!ok(tempx+dx[i], tempy+dy[i]))
break;

if(map[tempy+dy[i]][tempx+dx[i]] == GOAL)
{
if(step < minStep)
minStep = step+1;
return;
}

if(map[tempy+dy[i]][tempx+dx[i]] == BLOCK)
{
map[tempy+dy[i]][tempx+dx[i]] = VACANT;
dfs(tempx, tempy, step+1);
map[tempy+dy[i]][tempx+dx[i]] = BLOCK;
break;
}
tempx += dx[i];
tempy += dy[i];
}
}
}

int main()
{
while(scanf("%d%d", &w, &h) && w)
{
for(int i = 0; i < h; i++)
for(int j = 0; j < w; j++)
{
scanf("%d", &map[i][j]);
if(map[i][j] == 2)
startx = j, starty = i;
}

minStep = 11;
dfs(startx, starty, 0);
if(minStep < 11)
printf("%d/n", minStep);
else
printf("-1/n");
}
return 0;
}