This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include<bits/stdc++.h>
using namespace std;
const int N = 6e6;
const int inf = 2e9;
int k,n,m,sx,sy,ex,ey;
int d[8][2] = {{1,0},{-1,0},{0,1},{0,-1},{1,1},{1,-1},{-1,1},{-1,-1}};
int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int ans = inf;
    cin>>n>>m>>k;
    cin>>sx>>sy>>ex>>ey;
    vector<vector <char>> v(n + 2,vector<char>(m + 2,0));
    vector<vector <vector<bool>>> vis(n + 2,vector<vector<bool>>(m + 2,vector<bool>(2,0)));
    vector <array<int,2>> q;
    vector <array<int,4>> q2;
    for(int i = 0;i < n + 2;i++){
        v[i][0] = 2;
        v[i][m + 1] = 2;
    }
    for(int i = 0;i < m + 2;i++){
        v[0][i] = 2;
        v[n + 1][i] = 2;
    }
    for(int i = 0;i < n;i++){
        for(int j = 0;j < m;j++){
            char ch;
            cin>>ch;
            if(ch == '.'){
                v[i + 1][j + 1] = 0;
            }else{
                v[i + 1][j + 1] = 1;
            }
        }
    }
    vis[sx][sy][0] = 1;
    int g = 0;
    q.emplace_back(array<int,2>{sx,sy});
    for(int i = 0;i <= n + m;i++){
        int pt = 0;
        q2.clear();
        while(pt < q.size()){
            auto x = q[pt];pt++;g++;
            if(x[0] == ex && x[1] == ey){
                ans = i;
            }
            ///bfs
            if(!vis[x[0]][x[1]][1]){
                q2.emplace_back(array<int,4>{x[0],x[1],0,0});
            }
            for(int j = 0;j < 4;j++){
                int nx = x[0] + d[j][0];
                int ny = x[1] + d[j][1];
                if(!vis[nx][ny][0] && v[nx][ny] == 0){
                    vis[nx][ny][0] = 1;
                    q.emplace_back(array<int,2>{nx,ny});
                }
            }
        }
        q.clear();
        pt = 0;
        while(pt < q2.size()){
            auto x = q2[pt];pt++;g++;
            if(!vis[x[0]][x[1]][0]){
                q.emplace_back(array<int,2>{x[0],x[1]});
                vis[x[0]][x[1]][0] = 1;
            }
            if(x[2] != k - 1){
                for(int j = 0;j < 2;j++){
                    int nx = x[0] + d[j][0];
                    int ny = x[1] + d[j][1];
                    if(!vis[nx][ny][1] && v[nx][ny] != 2){
                        vis[nx][ny][1] = 1;
                        q2.emplace_back(array<int,4>{nx,ny,x[2] + 1,x[3]});
                    }
                }
            }
        }
        pt = 0;
        while(pt < q2.size()){
            auto x = q2[pt];pt++;g++;
            if(!vis[x[0]][x[1]][0]){
                q.emplace_back(array<int,2>{x[0],x[1]});
                vis[x[0]][x[1]][0] = 1;
            }
            if(x[3] != k - 1){
                for(int j = 2;j < 4;j++){
                    int nx = x[0] + d[j][0];
                    int ny = x[1] + d[j][1];
                    if(!vis[nx][ny][1] && v[nx][ny] != 2){
                        vis[nx][ny][1] = 1;
                        q2.emplace_back(array<int,4>{nx,ny,x[2],x[3] + 1});
                    }
                }
            }
            for(int j = 0;j < 4;j++){
                int nx = x[0] + d[j][0];
                int ny = x[1] + d[j][1];
                if(!vis[nx][ny][0] && v[nx][ny] != 2){
                    vis[nx][ny][0] = 1;
                    q.emplace_back(array<int,2>{nx,ny});
                }
            }
        }
    }
    assert(g <= 3*N);
    cout<<ans<<'\n';
    return 0;
}
Compilation message (stderr)
Main.cpp: In function 'int main()':
Main.cpp:42:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::array<int, 2> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   42 |         while(pt < q.size()){
      |               ~~~^~~~~~~~~~
Main.cpp:62:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::array<int, 4> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   62 |         while(pt < q2.size()){
      |               ~~~^~~~~~~~~~~
Main.cpp:80:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::array<int, 4> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   80 |         while(pt < q2.size()){
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