Kth Manhattan Distance Neighbourhood

• Time : $O(nmk)$
• Space : $O(nmk)$

vector<vector<int> > Solution::solve(int A, vector<vector<int>> &B) {
    int n = B.size(), m = B[0].size();
    vector<vector<int>> res = B;
    queue<array<int,5>> q;
    for(int i = 0; i < B.size(); i++) {
        for(int j = 0; j < B[0].size(); j++) {
            q.push({B[i][j], i, j, i, j});
        }
    }
    int dy[4]{-1,0,1,0}, dx[4]{0,1,0,-1};
    while(q.size()) {
        auto [v,y,x,oy,ox] = q.front(); q.pop();
        for(int i = 0; i < 4; i++) {
            int ny = y + dy[i], nx = x + dx[i];
            if(0 <= ny and ny < n and 0 <= nx and nx < m and res[ny][nx] < v and abs(ny-oy) + abs(nx - ox) <= A) {
                res[ny][nx] = v;
                q.push({v,ny,nx,oy,ox});
            }
        }
    }
    
    return res;
}