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], ]
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public class Solution { /**This code is an implemenatation of bfs idea.<br> * @author Averill Zheng * @version 2014-06-05 * @since JDK 1.7 */ public
List<List<Integer>> combine(int
n, int k) { List<List<Integer> > combinations = new
ArrayList<List<Integer> >(); if(k > 0){ for(int
i = 0; i < n; ++i){ List<Integer> aList = new
ArrayList<Integer>(); aList.add(i + 1); combinations.add(aList); } if(k > 1){ for(int
j = 1; j < k; ++j){ //j denotes the number of integer in each list List<List<Integer>> temp = new
ArrayList<List<Integer> >(); int
length = combinations.size(); for(int
l = 0; l < length; ++l){ List<Integer> aList = combinations.get(l); int
lastNumber = aList.get(j - 1); if(n - lastNumber >= k - j){ // has enough number to get the k combinations for(int
m = lastNumber + 1; m <= n; ++m){ List<Integer> newList = new
ArrayList<Integer>(); newList.addAll(aList); newList.add(m); temp.add(newList); } } } combinations = temp; } } } return
combinations; }} |
leetcode--Combinations,布布扣,bubuko.com
原文地址：http://www.cnblogs.com/averillzheng/p/3773977.html
