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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], ]
public static void main(String args[]) {
List<List<Integer>> list = combine(5, 2);
System.out.println(list.size());
for (List<Integer> alist : list)
System.out.println(alist + "*");
}
static public List<List<Integer>> combine(int n, int k) {
List<List<Integer>> list = new ArrayList<List<Integer>>();
if (n <= 0 || k > n)
return list;
dfs(list, n, k, 0);
return list;
}
static List<Integer> alist = new ArrayList<Integer>();
static void dfs(List<List<Integer>> list, int n, int k, int depth) {
if (depth >= k) {
list.add(new ArrayList<Integer>(alist));
return;
}
if (depth == 0)
for (int i = 1; i <= n - k + 1; i++) {
alist.add(i);
dfs(list, n, k, depth + 1);
alist.remove(alist.size() - 1);
}
else
for (int i = 1; i <= n - alist.get(alist.size() - 1) + k - depth - 1; i++) {
alist.add(alist.get(alist.size() - 1) + i);
dfs(list, n, k, depth + 1);
alist.remove(alist.size() - 1);
}
}
Java for LeetCode 077 Combinations
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原文地址：http://www.cnblogs.com/tonyluis/p/4513126.html
