codeforce-B. Fox And Two Dots
2016-08-14 15:08
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B. Fox And Two Dots
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
Fox Ciel is playing a mobile puzzle game called "Two Dots". The basic levels are played on a board of size n × m cells, like
this:
![](http://codeforces.com/predownloaded/40/54/4054f56d341c153a25dbc44b4a1e613d802d0149.png)
Each cell contains a dot that has some color. We will use different uppercase Latin characters to express different colors.
The key of this game is to find a cycle that contain dots of same color. Consider 4 blue dots on the picture forming a circle as an example. Formally, we call a sequence of dots d1, d2, ..., dk a cycle if
and only if it meets the following condition:
These k dots are different: if i ≠ j then di is
different from dj.
k is at least 4.
All dots belong to the same color.
For all 1 ≤ i ≤ k - 1: di and di + 1 are
adjacent. Also, dk and d1 should
also be adjacent. Cells x and y are
called adjacent if they share an edge.
Determine if there exists a cycle on the field.
Input
The first line contains two integers n and m (2 ≤ n, m ≤ 50):
the number of rows and columns of the board.
Then n lines follow, each line contains a string consisting of m characters,
expressing colors of dots in each line. Each character is an uppercase Latin letter.
Output
Output "Yes" if there exists a cycle, and "No"
otherwise.
Examples
input
output
input
output
input
output
input
output
input
output
Note
In first sample test all 'A' form a cycle.
In second sample there is no such cycle.
The third sample is displayed on the picture above ('Y' = Yellow, 'B'
= Blue, 'R' = Red).
一题我用的是dfs 其实仔细想想,你会发现从一个点跑,你可以想象一下其实dfs就像一只会分身
的老鼠,到达一个点只要四周可以跑,就会分身,一直跑下去,只要存在一个回路,它就会发现已经走过
然后就会汇报有回路,如果跑到最后都没有回路,说明从这个点和所有跑过的路都不会有回路,因为只要
存在回路,它就会发现其他老鼠跑过的路 值得注意的时不要走回路
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
Fox Ciel is playing a mobile puzzle game called "Two Dots". The basic levels are played on a board of size n × m cells, like
this:
![](http://codeforces.com/predownloaded/40/54/4054f56d341c153a25dbc44b4a1e613d802d0149.png)
Each cell contains a dot that has some color. We will use different uppercase Latin characters to express different colors.
The key of this game is to find a cycle that contain dots of same color. Consider 4 blue dots on the picture forming a circle as an example. Formally, we call a sequence of dots d1, d2, ..., dk a cycle if
and only if it meets the following condition:
These k dots are different: if i ≠ j then di is
different from dj.
k is at least 4.
All dots belong to the same color.
For all 1 ≤ i ≤ k - 1: di and di + 1 are
adjacent. Also, dk and d1 should
also be adjacent. Cells x and y are
called adjacent if they share an edge.
Determine if there exists a cycle on the field.
Input
The first line contains two integers n and m (2 ≤ n, m ≤ 50):
the number of rows and columns of the board.
Then n lines follow, each line contains a string consisting of m characters,
expressing colors of dots in each line. Each character is an uppercase Latin letter.
Output
Output "Yes" if there exists a cycle, and "No"
otherwise.
Examples
input
3 4 AAAA ABCA AAAA
output
Yes
input
3 4 AAAA ABCA AADA
output
No
input
4 4 YYYR BYBY BBBY BBBY
output
Yes
input
7 6 AAAAAB ABBBAB ABAAAB ABABBB ABAAAB ABBBAB AAAAAB
output
Yes
input
2 13 ABCDEFGHIJKLM NOPQRSTUVWXYZ
output
No
Note
In first sample test all 'A' form a cycle.
In second sample there is no such cycle.
The third sample is displayed on the picture above ('Y' = Yellow, 'B'
= Blue, 'R' = Red).
一题我用的是dfs 其实仔细想想,你会发现从一个点跑,你可以想象一下其实dfs就像一只会分身
的老鼠,到达一个点只要四周可以跑,就会分身,一直跑下去,只要存在一个回路,它就会发现已经走过
然后就会汇报有回路,如果跑到最后都没有回路,说明从这个点和所有跑过的路都不会有回路,因为只要
存在回路,它就会发现其他老鼠跑过的路 值得注意的时不要走回路
<span style="font-family:SimSun;">#include<cstdio> #include<cstring> char s[100][100]; int vis[100][100];//用于标记 int n,m;//n行m列 int flag; int dx[4]={1,-1,0,0}; int dy[4]={0,0,1,-1}; int judge(int a,int b) { if(a>=0&&a<n&&b>=0&&b<m) return 1; return 0; } void dfs(int x,int y,char o,int xx,int yy)//记录上一步走的路 { int i; for(i=0;i<4;++i) { int ex=x+dx[i]; int ey=y+dy[i]; if(judge(ex,ey)&&s[ex][ey]==o) { if(ex==xx&&ey==yy) continue; if(vis[ex][ey]) { flag=1; return ; } vis[ex][ey]=1; dfs(ex,ey,o,x,y); } } } int main() { scanf("%d%d",&n,&m); int i,j; for(i=0;i<n;++i) scanf("%s",s[i]);//这样就很容易形成地图 memset(vis,0,sizeof(vis)); for(i=0;i<n;++i) for(j=0;j<m;++j) { if(!vis[i][j]) { flag=0; vis[i][j]=1; dfs(i,j,s[i][j],-1,-1); if(flag) { printf("Yes\n"); return 0; } } } printf("No\n"); return 0; } </span>
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