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add some explaination

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This commit is contained in:
Hao Chen 2014-11-17 11:08:06 +08:00
parent 3dec9c4094
commit dff39d00a4
1 changed files with 44 additions and 9 deletions
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53
src/nextPermutation/nextPermutation.cpp
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@ -22,15 +22,44 @@
**********************************************************************************/
/*
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
...
*/
* 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 as below:
*
* 1) find the first place which num[i-1] < num[i]
* 2) find the first number from n-1 to i which >= num[i-1]
* 3) swap the 2) num with 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>
@ -40,6 +69,7 @@
#include <algorithm>
using namespace std;
void nextPermutation(vector<int> &num) {
if(num.size()<=1) return;
@ -54,10 +84,15 @@ void nextPermutation(vector<int> &num) {
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;
}