Can someone tell me what am I doing wrong?
Problem: Problem - B - Codeforces
Editorial: Codeforces Beta Round #22 Tutorial - Codeforces ( I followed the DP solution O((n*m)^2) )
Eg:
00001
00000
10100 //ans is 12
####1
####0
10100
My approach: rectangle with coordinates (x1, y1, x2, y2) is correct if and only if rectangles (x1, y1, x2-1, y2) and (x1, y1, x2, y2-1) are correct, and board[x2][y2] = β0β.
ie: dp[x1][y1][x2][y2]=(dp[x1][y1][x2-1][y2] && dp[x1][y1][x2][y2-1] && (board[x2][y2]==0))
If it is correct then find itβs perimeter (perimeter = 2*(x2-x1+y2-y1+2)) ie ans=max(ans,perimeter)
And dp[x1][y1][x2][y2]=1 for all i,j when board[x2][y2]==0. Because from point p1 to point p1, ie the same point always have a perimeter is the base case.
signed main(){
int r,c;cin>>r>>c;
vector<vi> v(r,vi(c));
bool dp[25][25][25][25]={false};//i,j to p,q
for(int i=0;i<r;i++){
string s;cin>>s;
for(int j=0;j<c;j++){
v[i][j]=(s[j]-'0');
if(v[i][j]==0)dp[i][j][i][j]=true;
}
}
int ans=-1;
for(int i=0;i<r;i++){//x1
for(int j=0;j<c;j++){//y1
for(int p=i;p<r;p++){//x2
for(int q=j;q<c;q++){//y2
//i,j to p,q , 0,0 0,2, afrom 1 to p, b from 1 to q
if(!(i==p && j==q)){
if(p-1>=0 && q-1>=0)
dp[i][j][p][q]=(dp[i][j][p-1][q] && dp[i][j][p][q-1] && (v[p][q]==0));
//cout<<dp[i][j][p][q]<<i<<j<<p<<q<<"\n";
if(dp[i][j][p][q]==true){
ans=max(ans,2*(p-i+q-j+2));
//cout<<"^";
}
}
}
}
}
}
cout<<ans;
}