29
07/2015
[LeetCode] Combinations
Combinations
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], ]
解题思路：
这道题的题意是找到1-n的数字中找出k个数的所有组合。可以采用递归回溯法。比较简单。
class Solution {
public:
vector<vector<int>> combine(int n, int k) {
vector<vector<int>> result;
if(n < 0 || k < 0 || n < k){
return result;
}
vector<int> item;
combineHelper(n, k, item, result);
return result;
}
void combineHelper(int n, int k, vector<int> item, vector<vector<int>>& result){
int size = item.size();
if(size>=k){
result.push_back(item);
return;
}
int last = size==0 ? 0 : item[size - 1];
if(n - last + size < k){ //无法达到k的大小了
return;
}
for(int i = last + 1; i <= n; i++){
item.push_back(i);
combineHelper(n, k, item, result);
item.pop_back();
}
}
};转载请注明：康瑞部落 » [LeetCode] Combinations
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