Tontti

#include <iostream>
using namespace std;
 
int n, m, x;
 
string f[2020];
int fi[2020][2020];
 
int sv[2020][2020];
int sh[2020][2020];
int sb[2020][2020];
 
 
int ilen(int a){
  int r=1; a/=10;
  while (a){ ++r; a/=10;}
  return r;
}
 
 
int main(){
  ios_base::sync_with_stdio(0); cin.tie(0);
 
  cin >> n >> m >> x;
  
  for (int i=0; i<n; ++i)cin >> f[i];
  
  for (int i=1; i<=n; ++i) for (int j=1; j<=m; ++j) fi[i][j]=(f[i-1][j-1]=='*')?1:0;
  
  
  for (int i=1; i<=n; ++i)
    for (int j=1; j<=m; ++j) sv[i][j]=sv[i][j-1]+fi[i][j];
    
  for (int j=1; j<=m; ++j)
    for (int i=1; i<=n; ++i) sh[i][j]=sh[i-1][j]+fi[i][j];
  
  for (int i=1; i<=n; ++i)
    for (int j=1; j<=m; ++j)
      sb[i][j]=sb[i-1][j-1]+sv[i][j-1]+sh[i-1][j]+fi[i][j];
  
 
  
  unsigned int ans=0;
  for (int i=1; i<=n; ++i){
    for (int j=1; j<=m; ++j){
      int a0=0; int b0=min(n-i, m-j);
      while (a0<b0){
        int md=(a0+b0)/2;
        if (sb[i-1][j-1]+sb[i+md][j+md]-sb[i-1][j+md]-sb[i+md][j-1]<x)
          a0=md+1;
        else
          b0=md;
      }
      if (sb[i-1][j-1]+sb[i+a0][j+a0]-sb[i-1][j+a0]-sb[i+a0][j-1]<x) ++a0;
      
      int a1=0; int b1=min(n-i, m-j);
      while (a1<b1){
        int md=(a1+b1+1)/2;
        if (sb[i-1][j-1]+sb[i+md][j+md]-sb[i-1][j+md]-sb[i+md][j-1]>x)
          b1=md-1;
        else
          a1=md;
      }
      if (sb[i-1][j-1]+sb[i+a1][j+a1]-sb[i-1][j+a1]-sb[i+a1][j-1]>x) --a1;
      ans+=a1+1-a0;
    }
  }
  cout << ans << "\n";
}

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 2

Verdict: ACCEPTED

Test 7

Group: 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 3

Verdict: ACCEPTED

Test 12

Group: 3

Verdict: ACCEPTED

Test 13

Group: 3

Verdict: ACCEPTED

Test 14

Group: 3

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: ACCEPTED