Lecture 05 - Array Part 2

Array

• & → Address of

  eg - & Myarray[0] = Myarray = 100

• * → Value at

  eg - * (Myarray) = 5

  * (Myarray + 1) = 10

Let ‘a’ be the name of the array -

• *a = *(a+0) = a[0] = 5;

  *(a+2) = a[2] = 15;

  (a+i) = Base address + i * (size of datatype)

• a + i = i + a

  a[i]= *(a+i) = *(i+a) = i[a]

2-D Array

int a [m] [n];

• ( a [i] [j] ) = *(a[i] + j ) = *(*(a+i) + j )

Examples

Leetcode 463 - island Parameter

#include <iostream>
#include <vector>
using namespace std;
int islandPerimeter(vector<vector<int>>& grid) {
    int m = grid.size();
    int n = grid[0].size();
    int p=0;
    for(int i=0;i<m;i++){
        for(int j=0;j<n;j++){
            if(grid[i][j]==1){
                if(i == 0 || grid[i-1][j] == 0) p++;
                if(i == m-1 || grid[i+1][j] == 0) p++;
                if(j == 0 || grid[i][j-1] == 0) p++;
                if(j == n-1 || grid[i][j+1] == 0) p++;
            }
        }
    }
    return p;
}
int main(){
    vector<vector<int>> grid = {{0,1,0,0},{1,1,1,0},{0,1,0,0}};
    int p = islandPerimeter(grid);   
    cout << p; 
    return 0;
}
// this took very much time but i get it now (i was getting consufed on fundamentals)
// i was assuming that left if a[i-1][j] but it is top 
// this was for all the directions