# QUESTION

Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.

If such arrangement is not possible, it must rearrange it as the lowest possible order (ie, sorted in ascending order).

The replacement must be in-place, do not allocate extra memory.

Here are some examples. Inputs are in the left-hand column and its corresponding outputs are in the right-hand column.

- 1,2,3 → 1,3,2
- 3,2,1 → 1,2,3
- 1,1,5 → 1,5,1

This question is provided by LeetCode.

# SOLUTION

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class Solution { public: void nextPermutation(vector<int> &num) { // Start typing your C/C++ solution below // DO NOT write int main() function if (num.size() <= 1) return; int i = num.size() - 1; int j; while (i > 0 && num[i - 1] >= num[i]) { --i; } if (i == 0) { reverse(num.begin(), num.end()); return; } --i; j = i + 1; while (j < num.size() && num[j] > num[i]) { ++j; } --j; num[i] ^= num[j]; num[j] ^= num[i]; num[i] ^= num[j]; reverse(num.begin() + i + 1, num.end()); } }; |

Xor operation is not good for swap, especially on array elements. Although it looks very fancy.

I have written a post that talking about the issue:

Xor Swap IssueFor Performance purpose and correctness, it’s better to use simplest swap with third temporary variable. Or just call swap function in C++ library.