2014-10-20 11:23:39 +08:00
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// Source : https://oj.leetcode.com/problems/permutations/
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// Author : Hao Chen
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// Date : 2014-06-21
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2014-10-21 10:49:57 +08:00
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/**********************************************************************************
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*
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* Given a collection of numbers, return all possible permutations.
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*
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* For example,
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* [1,2,3] have the following permutations:
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* [1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1].
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*
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*
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**********************************************************************************/
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2014-10-20 11:23:39 +08:00
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#include <stdio.h>
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#include <stdlib.h>
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#include <iostream>
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#include <vector>
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using namespace std;
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/*
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{ 1 2 3 }
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{ 2 1 3 }
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{ 3 2 1 }
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{ 1 3 2 }
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{ 2 3 1 }
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{ 3 1 2 }
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*/
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2014-10-27 22:43:09 +08:00
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/*
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* The algroithm - Take each element in array to the first place.
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*
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* For example:
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*
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* 0) initalization
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*
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* pos = 0
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* [1, 2, 3]
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*
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* 1) take each element into the first place,
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*
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* pos = 1
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* [1, 2, 3] ==> [2, 1, 3] , [3, 1, 2]
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*
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* then we have total 3 answers
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* [1, 2, 3], [2, 1, 3] , [3, 1, 2]
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*
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* 2) take each element into the "first place" -- pos
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*
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* pos = 2
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* [1, 2, 3] ==> [1, 3, 2]
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* [2, 1, 3] ==> [2, 3, 1]
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* [3, 1, 2] ==> [3, 2, 1]
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*
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* then we have total 6 answers
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* [1, 2, 3], [2, 1, 3] , [3, 1, 2], [1, 3, 2], [2, 3, 1], [3, 2, 1]
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*
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* 3) pos = 3 which greater than length of array, return.
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*
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*/
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2014-10-20 11:23:39 +08:00
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vector<vector<int> > permute(vector<int> &num) {
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vector<vector<int> > vv;
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vv.push_back(num);
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if (num.size() <2){
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return vv;
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}
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int pos=0;
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while(pos<num.size()-1){
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int size = vv.size();
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for(int i=0; i<size; i++){
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2014-10-27 22:43:09 +08:00
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//take each number to the first place
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2014-10-20 11:23:39 +08:00
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for (int j=pos+1; j<vv[i].size(); j++) {
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vector<int> v = vv[i];
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int t = v[j];
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v[j] = v[pos];
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v[pos] = t;
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vv.push_back(v);
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}
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}
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pos++;
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}
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return vv;
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}
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int main(int argc, char** argv)
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{
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int n = 3;
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if (argc>1){
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n = atoi(argv[1]);
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}
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vector<int> v;
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for (int i=0; i<n; i++) {
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v.push_back(i+1);
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}
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vector<vector<int> > vv;
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vv = permute(v);
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for(int i=0; i<vv.size(); i++) {
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cout << "{ ";
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for(int j=0; j<vv[i].size(); j++){
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cout << vv[i][j] << " ";
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}
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cout << "}" <<endl;
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}
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return 0;
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}
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