leetcode/src/combinations/combinations.cpp at master · ourstart/leetcode · GitHub

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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);

}

leetcode/src/combinations/combinations.cpp at master · ourstart/leetcode · GitHub

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