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136 lines (118 loc) · 3.17 KB
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// Source : https://oj.leetcode.com/problems/combinations/
// Author : Hao Chen
// Date : 2014-07-03
/**********************************************************************************
*
* Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.
*
* For example,
* If n = 4 and k = 2, a solution is:
*
* [
* [2,4],
* [3,4],
* [2,3],
* [1,2],
* [1,3],
* [1,4],
* ]
*
*
**********************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
void getCombination(int n, int k, vector<int>& solution, vector< vector<int> >& result );
vector<vector<int> > combine1(int n, int k);
vector<vector<int> > combine2(int n, int k);
vector<vector<int> > combine(int n, int k) {
if (random()%2){
cout << "recusive method!" << endl;
return combine1(n, k);
}
cout << "non-recusive method!" << endl;
return combine2(n, k);
}
vector<vector<int> > combine1(int n, int k) {
vector<vector<int> > result;
vector<int> solution;
getCombination(n, k, solution, result);
return result;
}
void getCombination(int n, int k, vector<int>& solution, vector< vector<int> >& result ){
if (k==0){
//sort to meet LeetCode requirement
vector<int> v = solution;
sort(v.begin(), v.end());
result.push_back(v);
return;
}
for(int i=n; i>0; i--){
solution.push_back(i);
getCombination(i-1, k-1, solution, result);
solution.pop_back();
}
}
vector<vector<int> > combine2(int n, int k) {
vector<vector<int> > result;
vector<int> d;
for (int i=0; i<n; i++){
d.push_back( (i<k) ? 1 : 0 );
}
//1) from the left, find the [1,0] pattern, change it to [0,1]
//2) move all of the 1 before the pattern to the most left side
//3) check all of 1 move to the right
while(1){
vector<int> v;
for(int x=0; x<n; x++){
if (d[x]) v.push_back(x+1);
}
result.push_back(v);
//step 1), find [1,0] pattern
int i;
bool found = false;
int ones =0;
for(i=0; i<n-1; i++){
if (d[i]==1 && d[i+1]==0){
d[i]=0; d[i+1]=1;
found = true;
//step 2) move all of right 1 to the most left side
for (int j=0; j<i; j++){
d[j]=( ones > 0 ) ? 1 : 0;
ones--;
}
break;
}
if (d[i]==1) ones++;
}
if (!found){
break;
}
}
return result;
}
void printResult(vector<vector<int> >& result)
{
for(int i=0; i<result.size(); i++){
cout << "{";
for(int j=0; j<result[i].size(); j++){
cout << " " << result[i][j];
}
cout << " }" <<endl;
}
}
int main(int argc, char** argv)
{
srand(time(NULL));
int n = 4, k =2;
if (argc>2){
n = atoi(argv[1]);
k = atoi(argv[2]);
}
vector<vector<int> > r = combine(n, k);
printResult(r);
}