PeterNaut's blog

How to swap two matrixes in O(1) C++
By PeterNaut, 11 years ago, In English

In order to swap two arrays in O(1) you can do this using pointers:

#include <algorithm>
int AA[100], *A=AA, BB[100], *B=BB;
swap(A, B);

But how can you do that for matrixes in C++?

Tags c++
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11 years ago, # |
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First, you do not need to make *A and *B. swap (AA,BB) will do.

Second, matrices are just arrays too so they can be swapped too in constant time. (even if array elements are dynamically created using new keyword).

Lastly, if you still do not believe something; vectors make it more convenient

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11 years ago, # |
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You do it the same way:

int AA[100][100], (*A)[100]=AA, BB[100][100], (*B)[100]=BB;    
swap(A, B);

int (*)[100] is a pointer to an array of 100 ints. It may be easier to define a struct containing the array, and use pointers to such objects.

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    11 years ago, # ^ |
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    Thanks! But why do you need the paranthesis in (*A)[100]=AA?

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      11 years ago, # ^ |
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      int (*A)[100] is a pointer to an array of 100 ints. int *A[100] is an array of 100 pointers to ints. You can google for "c declaratons" for more reading.

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