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// Source : https://oj.leetcode.com/problems/next-permutation/

// Author : Hao Chen

// Date : 2014-08-21

/**********************************************************************************

*

* 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

*

**********************************************************************************/

/*

* Take a look the following continuous permutation, can you find the patern?

*

* 1 2 3 4

* 1 2 4 3

* 1 3 2 4

* 1 3 4 2

* 1 4 2 3

* 1 4 3 2

* 2 1 3 4

* ...

*

* The pattern can be descripted as below:

*

* 1) from n-1 to 0, find the first place [i-1] which num[i-1] < num[i]

* 2) from n-1 to i, find the first number from n-1 to i which >= num[i-1]

* 3) swap the 2) num with the num[i-1]

* 4) sort the sub-array [i, n) //actuall sort is fine as well

*

* For example:

*

* 1 4 3 2 <-- 1) find the first place which num[i-1] < num[i]

* ^

*

* 1 4 3 2 <-- 2) find the first number from n-1 to i which >= num[i-1]

* ^ ^

*

* 2 4 3 1 <-- 3) swap them

* ^ ^

*

* 2 4 3 1 <-- 4) sort

* ^ ^

*

* 2 1 3 4

*

* Edge Case:

*

* 4 3 2 1, the next permutation is 1 2 3 4

*/

#include <stdio.h>

#include <stdlib.h>

#include <iostream>

#include <vector>

#include <algorithm>

using namespace std;

void nextPermutation(vector<int> &num) {

if(num.size()<=1) return;

for(int i=num.size()-1; i>0; i--) {

if (num[i-1] < num[i]){

int j = num.size()-1;

while( num[i-1] >= num[j]) {

//pass;

j--;

}

int tmp = num[j];

num[j] = num[i-1];

num[i-1] = tmp;

//sort works as well

//sort(num.begin()+i, num.end());

reverse(num.begin()+i, num.end());

return;

}

//edge case: 4 3 2 1

if (i == 1 ){

//sort works as well

//sort(num.begin(), num.end());

reverse(num.begin(), num.end());

return;

}

}

}

void printVector(vector<int> &num) {

for(int i=0; i<num.size(); i++) {

cout << num[i] << " ";

}

cout <<endl;

}

bool isBeginVector(vector<int> &num) {

for(int i=0; i<num.size(); i++) {

if(num[i] != i+1) {

return false;

}

}

return true;

}

int main(int argc, char** argv)

{

int n = 4;

if (argc>1){

n = atoi(argv[1]);

}

vector<int> num;

for(int i=1; i<=n; i++){

num.push_back(i);

}

while(true){

printVector(num);

nextPermutation(num);

if(isBeginVector(num)){

break;

}

}

return 0;

}