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POJ1753 Flip Game【DFS】

沪钢木子 2022-07-27 阅读 35



Flip Game


Time Limit: 1000MS

 

Memory Limit: 65536K

Total Submissions: 27221

 

Accepted: 11809


Description


Flip game is played on a rectangular 4x4 field with two-sided pieces placed on each of its 16 squares. One side of each piece is white and the other one is black and each piece is lying either it's black or white side up. Each round you flip 3 to 5 pieces, thus changing the color of their upper side from black to white and vice versa. The pieces to be flipped are chosen every round according to the following rules: 

  1. Choose any one of the 16 pieces.
  2. Flip the chosen piece and also all adjacent pieces to the left, to the right, to the top, and to the bottom of the chosen piece (if there are any).


POJ1753 Flip Game【DFS】_ide

Consider the following position as an example: 



bwbw 


wwww 


bbwb 


bwwb 


Here "b" denotes pieces lying their black side up and "w" denotes pieces lying their white side up. If we choose to flip the 1st piece from the 3rd row (this choice is shown at the picture), then the field will become: 



bwbw 


bwww 


wwwb 


wwwb 


The goal of the game is to flip either all pieces white side up or all pieces black side up. You are to write a program that will search for the minimum number of rounds needed to achieve this goal. 



Input


The input consists of 4 lines with 4 characters "w" or "b" each that denote game field position.


Output


Write to the output file a single integer number - the minimum number of rounds needed to achieve the goal of the game from the given position. If the goal is initially achieved, then write 0. If it's impossible to achieve the goal, then write the word "Impossible" (without quotes).


Sample Input


bwwb bbwb bwwb bwww


Sample Output


4


Source


​​Northeastern Europe 2000​​



# include<stdio.h>
# include<string.h>

char pan[4][4];
int change[4][4];

void flip(int i,int j)
{
if(change[i][j]==1)
change[i][j] = 0;
else
change[i][j] = 1;

if(i<3)
if(change[i+1][j]==1)
change[i+1][j] = 0;
else
change[i+1][j] = 1;
if(i>0)
if(change[i-1][j]==1)
change[i-1][j] = 0;
else
change[i-1][j] = 1;
if(j<3)
if(change[i][j+1]==1)
change[i][j+1] = 0;
else
change[i][j+1] = 1;
if(j>0)
if(change[i][j-1]==1)
change[i][j-1] = 0;
else
change[i][j-1] = 1;
}

int main()
{
int i,j,k,num,min;
int state[5];
memset(pan,0,sizeof(pan));
memset(state,0,sizeof(state));

for(i=0;i<4;i++)
{
for(j=0;j<4;j++)
{
scanf("%c",&pan[i][j]);
}
getchar();
}
min = 17;
for(k=0;k<16;k++)
{
memset(change,0,sizeof(change));

for(i=0;i<4;i++)
{
for(j=0;j<4;j++)
{
if(pan[i][j]=='w')
{
change[i][j] = 0;
}
else
{
change[i][j] = 1;
}
}
}

if(j>0)
state[0] +=1;
for(i=0;i<4;i++)
{
if(state[i]>=2)
{
state[i] -= 2;
state[i+1]++;
}
}
num = 0;
for(i=0;i<4;i++)
{
if(state[i]==1)
{
flip(0,i);
num++;
}
}

for(i=0;i<3;i++)
{
for(j=0;j<4;j++)
{
if(change[i][j]==0)
{
flip(i+1,j);
num++;
}
}
}
for(j=0;j<4;j++)
{
if(change[3][j]==1)
continue;
else
break;
}

if(j==4)
{
if(num<min)
min = num;
}

memset(change,0,sizeof(change));

for(i=0;i<4;i++)
{
for(j=0;j<4;j++)
{
if(pan[i][j]=='w')
{
change[i][j] = 0;
}
else
{
change[i][j] = 1;
}
}
}

num = 0;
for(i=0;i<4;i++)
{
if(state[i]==1)
{
flip(0,i);
num++;
}
}

for(i=0;i<3;i++)
{
for(j=0;j<4;j++)
{
if(change[i][j]==1)
{
flip(i+1,j);
num++;
}
}
}
for(j=0;j<4;j++)
{
if(change[3][j]==0)
continue;
else
break;
}

if(j==4)
{
if(num<min)
min = num;
}

}

if(min<17)
printf("%d\n",min);
else
printf("Impossible\n");


return 0;
}



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