Optional chaining (?.) in Javascript

 

The optional chaining ?. is a safe way to access nested object properties, even if a mid   property doesn’t exist.

As an example, let’s say we have person objects and most of person have addresses in person.address property, with the street person.address.street, but some did not provide them.

In such case, when we attempt to get person.address.street without having street ,we get an error:

 

let person = {

}

 

console.log(person.address.street)

//error

 

 

As there is no address in person, an attempt to get person.address.street fails with an error.

But we if use optional chaining , we will get undefined instead of error.

 

console.log(person?.address?.street)  // undefined

 

In many practical cases we’d prefer to get undefined instead of an error here (meaning “no street”).

 

One case would be like this ,

 

let street = person?.address?.street ?? ' No street' ;

 

 

 

Top View of Binary Tree using JavaScript

class Solution

{

    //Function to return a list of nodes visible from the top view 

    //from left to right in Binary Tree.

    topView(root)

    {

        //your code here

        let map = {} ;

        function f(root, hdis, level){

            if(root === null) return ;

            if(map[hdis] === undefined) {

                map[hdis] = [level, root.data] ;

            }else{

                if(level<map[hdis][0]){

                    map[hdis] = [level, root.data]

                }

            }

            f(root.left, hdis-1, level+1);

            f(root.right, hdis +1, level+1);

        }

        f(root, 0, 0);

       // console.log(map)

        let arr = [] , ans = [];

        for(let [key, value] of Object.entries(map)){

           // console.log(value)

            arr.push(key);

        }

        

        arr.sort((a,b)=>a-b);

       // console.log(arr)

        for(let i = 0;i<arr.length;i++){

            ans.push(map[arr[i]][1])

        }

        return ans;

    }

}

UVA 539 SOLUTION

#include<stdio.h>
#define READ freopen("input.txt","r",stdin)
#define WRITE freopen("output.txt","w",stdout)
#define ll long long
#define MAX(a,b)  a>b?a:b
#define siz 102
using namespace std ;

int node,edge,mx,path;
int adj[50][50] ;

void dfs(int cur)
{

    for(int i = 0; i< node; i++)
    {

        if(adj[cur][i]==1)
        {
            path++;
            adj[cur][i]= 0 ;
            adj[i][cur]= 0 ;
            dfs(i);
            adj[cur][i]= 1 ;
            adj[i][cur]= 1 ;
            path--;

        }
    }
       mx = MAX(mx,path) ;
}


int main()
{

  //  READ;
    while(scanf("%d %d",&node,&edge)==2)
    {
        if(node==0 && edge==0) break ;

        for(int i = 0 ; i<32; i++)
            for(int j = 0; j<32; j++) adj[i][j] = 0 ;

        // for(int i =0 ; i<=node; i++) mark[i] = false ;
        for(int i = 0; i<edge; i++)
        {
            int u,v;
            scanf("%d %d",&u,&v);
            adj[u][v] = 1 ;
            adj[v][u] = 1 ;
        }
        int ans = 0 ;
        for(int i = 0 ; i<node; i++)
        {
            mx = 0;
            dfs(i);
            ans = MAX(ans, mx) ;
        }
        printf("%d\n",ans) ;
    }

    return 0 ;
}

uva 260 solution

#include<stdio.h>
#define READ freopen("input.txt","r",stdin)
#define WRITE freopen("output.txt","w",stdout)
#define ll long long
#define Max(a,b) (a>b?a:b)
int x[]=  {-1,0,-1,0,1,1};
int y[] = {0,1,-1,-1,0,1};

char str[201][201];
bool visited[201][201];
int row ;
bool black ;

void dfs(int r,int c)
{
    if(r == 0) black  =true ;
    for(int i=0; i<6; i++)
    {
        int R = r+x[i];
        int C = c+y[i];
        if(R>=0 && R<row && C>=0 && C<row && visited[R][C]==false&&str[R][C]=='b')
        {
            visited[R][C] =true ;
            dfs(R,C);
        }
    }

}
void init()
{
    for(int i=0; i<201; i++)
        for(int j=0; j<201; j++) visited[i][j]= false ;
    black=false;
}
int main()
{
  //  READ ;
    int cnt = 0 ;
    while(scanf("%d",&row)==1 && row!=0)
    {
        init() ;
        for(int i = 0; i< row ; i++) scanf("%s",str[i]);

        for(int i=0; i<row; i++)
        {
            if(str[row-1][i]=='b')
            {
                dfs(row-1,i);
            }
        }
        if(black)printf("%d %c\n",++cnt,'B');
        else printf("%d %c\n",++cnt,'W');

    }


    return 0 ;
}

UVA 167

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
#define READ freopen("input.txt","r",stdin)
#define ll long long
int ary[9][9];
int chk[9][9];
int mx ;

int MAX(int a,int b)
{
    return a>b?a:b;
}

bool issafe(int row,int col)
{
    for(int i=0;i<8;i++)
    {
        if(chk[row][i]==1) return false ;
    }
    for(int i=0;i<=row;i++)
        if(chk[i][col]==1) return false;
    for(int i=row,j=col;i>=0 && j>=0;i--,j--)
    {
        if(chk[i][j]==1) return false;
    }
    for(int i=row,j=col;i>=0&& j<8;i--,j++)
    {
        if(chk[i][j]==1) return false;
    }
    return true;
}
void NQ(int r,int sum)
{
    if(r==8)
    {
        mx = MAX(mx,sum);
        return ;
    }
    for(int c = 0; c<8; c++)
    {
        if(issafe(r,c))
        {
            chk[r][c] =1;
            NQ(r+1,sum+ary[r][c]);
            chk[r][c] =0;
        }
    }
}
int main()
{
    READ ;
    int test ;
    scanf("%d",&test);
    while(test--)
    {
        for(int i=0; i<8; i++)
        {
            for(int j=0; j<8; j++) scanf("%d",&ary[i][j]);
        }
        mx = -1 ;
        //clear();
        NQ(0,0);
        printf("%5d\n",mx);
    }
    return 0;
}

UVA 280 SOLUTION

#include<stdio.h>
#define READ freopen("Text.txt","r",stdin)
#define ll long long

int node;
int graph[102][102];
int visited[102];

void clear(int node)
{
 for (int i = 0; i <= node; i++) visited[i] = 0;

}

void init_Graph()
{
 for (int i = 0; i < 101; i++)
  for (int j = 0; j < 102; j++) graph[i][j] = 0;
}
void dfs(int n)
{
 for (int i = 1; i <= node; i++)
 {
  if (graph[n][i] == 1 && visited[i] == 0)
  {
   visited[i] = 1;
   dfs(i);
  }
 }

 return;
}
int main()
{
 // READ;
 while (scanf("%d", &node) == 1 && node != 0)
 {
  int start, n, q, s;
  init_Graph();
  while (scanf("%d", &start) == 1 && start != 0)
  {
   while (scanf("%d", &n) && n != 0)
   {
    graph[start][n] = 1;
   }
  }
  scanf("%d", &q);
  while (q--)
  {
   scanf("%d", &s);
   int ans = 0;
   clear(node);
   dfs(s);
   for (int i = 1; i <= node; i++) if (visited[i] == 0) ans++;
   printf("%d", ans);
   for (int i = 1; i <= node; i++) if (visited[i] == 0)  printf(" %d", i);
   puts("");

  }

 }

 return 0;
}

uva 118 solution

#include<stdio.h>
#define ll long long
int row, col;
int ary[100][100];
char d[10], str[102];
int main()
{
 //freopen("Text.txt", "r", stdin);
 scanf("%d %d", &row, &col);

 for (int i = 0; i <= row; i++)
  for (int j = 0; j <= col; j++) ary[i][j] = 0;
 int r, c;
 while (scanf("%d %d %s", &r, &c, d) == 3)
 {
  scanf("%s", str);
  char dir = d[0];
  bool flag = true;
  for (int i = 0; str[i] != '\0'; i++)
  {
   if (str[i] == 'R' || str[i] == 'L')
   {
    //printf("%d\n",i+1);
    if (dir == 'E')
    {
     str[i] == 'R' ? dir = 'S' : dir = 'N';
    }
    else if (dir == 'N')
    {
     str[i] == 'R' ? dir = 'E' : dir = 'W';
    }
    else if (dir == 'S')
    {
     str[i] == 'R' ? dir = 'W' : dir = 'E';
    }
    else
    {
     str[i] == 'R' ? dir = 'N' : dir = 'S';
    }
    //printf("---%c----", dir);
   }
   else
   {
    if (dir == 'E')
    {
     if (r + 1 <= row) r += 1;
     else
     {
      if (ary[r][c] == 0)
      {
       ary[r][c] = 1;
       printf("%d %d %c LOST\n", r, c, dir);
       flag = false;
       break;
      }
      else continue;
     }
    }

    if (dir == 'N')
    {
     if (c + 1 <= col) c += 1;
     else
     {
      if (ary[r][c] == 0)
      {
       ary[r][c] = 1;
       printf("%d %d %c LOST\n", r, c, dir);
       flag = false;
       break;
      }
      else continue;
     }
    }

    if (dir == 'S')
    {
     if (c - 1 >= 0) c -= 1;
     else
     {
      if (ary[r][c] == 0)
      {
       ary[r][c] = 1;
       printf("%d %d %c LOST\n", r, c, dir);
       flag = false;
       break;
      }
      else continue;
     }
    }

    if (dir == 'W')
    {
     if (r - 1 >= 0) r -= 1;
     else
     {
      if (ary[r][c] == 0)
      {
       ary[r][c] = 1;
       printf("%d %d %c LOST\n", r, c, dir);
       flag = false;
       break;
      }
      else continue;
     }
    }

    //printf("%d %d\n", r, c);
   }
   // printf("%c\n",dir);
  }
  if (flag) printf("%d %d %c\n", r, c, dir);
 }

 return 0;
}