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