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Construct a linked list from 2D matrix (Iterative Approach) in C++
Suppose we have one matrix, we have to convert it to 2d linked list using iterative approach. The list will have the right and down pointer.
So, if the input is like
| 10 | 20 | 30 |
| 40 | 50 | 60 |
| 70 | 80 | 90 |
then the output will be
To solve this, we will follow these steps −
real_head := NULL
Define an array head_arr of size: m.
for initialize i := 0, when i < m, update (increase i by 1), do −
head_arr[i] := NULL
for initialize j := 0, when j < n, update (increase j by 1), do −
p := new tree node with value mat[i, j]
if real_head is null, then −
real_head := p
if head_arr[i] is null, then −
head_arr[i] := p
Otherwise
right of right_ptr := p
right_ptr := p
for initialize i := 0, when i < m - 1, update (increase i by 1), do −
p := head_arr[i], q = head_arr[i + 1]
while (p and q both are not null), do −
down of p := q
p := right of p
q := right of q
return real_head
Example
Let us see the following implementation to get better understanding −
#include <bits/stdc++.h>
using namespace std;
class TreeNode {
public:
int data;
TreeNode *right, *down;
TreeNode(int d){
data = d;
right = down = NULL;
}
};
void show_2d_list(TreeNode* head) {
TreeNode *right_ptr, *down_ptr = head;
while (down_ptr) {
right_ptr = down_ptr;
while (right_ptr) {
cout << right_ptr->data << " ";
right_ptr = right_ptr->right;
}
cout << endl;
down_ptr = down_ptr->down;
}
}
TreeNode* make_2d_list(int mat[][3], int m, int n) {
TreeNode* real_head = NULL;
TreeNode* head_arr[m];
TreeNode *right_ptr, *p;
for (int i = 0; i < m; i++) {
head_arr[i] = NULL;
for (int j = 0; j < n; j++) {
p = new TreeNode(mat[i][j]);
if (!real_head)
real_head = p;
if (!head_arr[i])
head_arr[i] = p;
else
right_ptr->right = p;
right_ptr = p;
}
}
for (int i = 0; i < m - 1; i++) {
TreeNode *p = head_arr[i], *q = head_arr[i + 1];
while (p && q) {
p->down = q;
p = p->right;
q = q->right;
}
}
return real_head;
}
int main() {
int m = 3, n = 3;
int mat[][3] = {
{ 10, 20, 30 },
{ 40, 50, 60 },
{ 70, 80, 90 } };
TreeNode* head = make_2d_list(mat, m, n);
show_2d_list(head);
}Input
{ { 10, 20, 30 },
{ 40, 50, 60 },
{ 70, 80, 90 } }Output
10 20 30 40 50 60 70 80 90
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