Combination Sum III问题及解法
2017-09-06 09:17
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问题描述:
Find all possible combinations of k numbers that add up to a number n, given that only numbers
from 1 to 9 can be used and each combination should be a unique set of numbers.
示例:
Input: k = 3, n = 7
Output:
Input: k = 3, n = 9
Output:
问题分析:
这是一类回溯法问题,我们可以考虑采用求组合的方法求解该问题(从1-9这9个数字中选取k个不同的数使它的和为n)
过程相见代码:
class Solution {
public:
vector<vector<int>> combinationSum3(int k, int n) {
vector<vector<int>> res;
vector<int> re;
bs(res, re, n, 1, k);
return res;
}
void bs(vector<vector<int>>&res, vector<int>& re,int n,int start,int k)
{
if (!n || !k)
{
if (!n && !k) res.push_back(re);
return;
}
for (int i = start; i <= 9; i++)
{
if (i > n) break;
re.emplace_back(i);
bs(res, re, n - i, i + 1,k - 1);
re.pop_back();
}
}
};
Find all possible combinations of k numbers that add up to a number n, given that only numbers
from 1 to 9 can be used and each combination should be a unique set of numbers.
示例:
Input: k = 3, n = 7
Output:
[[1,2,4]]
Input: k = 3, n = 9
Output:
[[1,2,6], [1,3,5], [2,3,4]]
问题分析:
这是一类回溯法问题,我们可以考虑采用求组合的方法求解该问题(从1-9这9个数字中选取k个不同的数使它的和为n)
过程相见代码:
class Solution {
public:
vector<vector<int>> combinationSum3(int k, int n) {
vector<vector<int>> res;
vector<int> re;
bs(res, re, n, 1, k);
return res;
}
void bs(vector<vector<int>>&res, vector<int>& re,int n,int start,int k)
{
if (!n || !k)
{
if (!n && !k) res.push_back(re);
return;
}
for (int i = start; i <= 9; i++)
{
if (i > n) break;
re.emplace_back(i);
bs(res, re, n - i, i + 1,k - 1);
re.pop_back();
}
}
};
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