sort 2d array

[LATCH100]

how would you sort int arr[3][3]= { { 2, 7, 6 }, { 9, 5, 1 }, {4,3,8} }; ?

[MiiNiPaa]

How should sorted array looks?

[LATCH100]

1,2,3,4,5,6,7,8,9

[MiiNiPaa]

So it is simple: std::sort(&arr[0][0], &arr[0][0] + 9);

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#include <iostream> #include <algorithm> int main() { int arr[3][3]= { { 2, 7, 6 }, { 9, 5, 1 }, {4,3,8} }; std::sort(&arr[0][0], &arr[0][0] + 9); for(auto& i: arr) for (auto j: i) std::cout << j << ' '; }

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[anup30]

@MiiNiPaa, how do you set code and output side by side ?

[MiiNiPaa]

@MiiNiPaa, how do you set code and output side by side ?

http://www.cplusplus.com/articles/z13hAqkS/

[xenovia12]

@MiiNiPaa

for(auto& i: arr)
		for (auto j: i)

what does auto means in for loop?
i just know about the auto storage class and the one that assumes the data type in c++11

[MiiNiPaa]

This is range-based-for loop.
http://en.cppreference.com/w/cpp/language/range-for
http://www.cprogramming.com/c++11/c++11-ranged-for-loop.html

Auto here means same thing like it does in variable declaration: let compiler deduct type of variable itself.

Without it you would need to write (reference to array of 3 ints) type yourself, which is not trivial for most. We need to make it reference, becuse you cannot pass arrays by value.

Variant without auto:

for(int(&i)[3]: arr)
	for (int j: i)
		std::cout << j << ' ';

[anup30]

std::sort(&arr[0][0], &arr[0][0] + 9);

std::sort(&arr[0][0], &arr[2][2]);

both requires #include <algorithm>

[MiiNiPaa]

std::sort(&arr[0][0], &arr[2][2]);

Not the same thing. Try it out.
If you want to get rid of magic numbers: std::sort(&arr[0][0], &arr[0][0] + sizeof(arr)/sizeof(int));

[anup30]

Not the same thing.

is there any difference?

[MiiNiPaa]

Yes.

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&arr[0][0], &arr[0][0] + 9 std::sort(&arr[0][0], &arr[2][2]);

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[anup30]

thanks.

[D80DSL3A]

Isn't the difference a matter of giving "one past the end" vs not?

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&arr[0][0], &arr[2][2]// last element &arr[0][0], &arr[2][3]// one past the end

123456798 123456789

[MiiNiPaa]

arr[2][3] is illegal. You cannot actually access one-past-the-end element legally.
Best you can do is: (arr[2] + 3).