63 lines
1.4 KiB
C++
63 lines
1.4 KiB
C++
#include <vector>
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#include <functional>
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#include <iostream>
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/**
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* 216. Combination Sum III
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* Find all valid combinations of k numbers that sum up to n such that the following conditions are true:
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*
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* Only numbers 1 through 9 are used.
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* Each number is used at most once.
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* Return a list of all possible valid combinations. The list must not contain the same combination twice, and the combinations may be returned in any order.
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*/
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class Solution {
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public:
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static std::vector<std::vector<int>> combinationSum3(int k, int n) {
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int current = 0;
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std::vector<int> work;
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std::vector<std::vector<int>> ret;
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work.reserve(k);
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std::function<void(int, int)> dfs = [&](int rem, int begin) {
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if (rem <= 1) {
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if (n - current > work.back() && n - current < 10) {
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ret.push_back(work);
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ret.back().push_back(n - current);
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}
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return;
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}
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for (int i = begin; i <= 9; current -= i++ /* On Exit */) {
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// On Entry
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current += i;
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// rem is at least 2.
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if (current + (rem - 1) * (i + 1) + (rem - 1) * (rem - 2) / 2 > n) {
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current -= i;
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break;
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}
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work.push_back(i);
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dfs(rem - 1, i + 1);
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work.pop_back();
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}
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};
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dfs(k, 1);
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return ret;
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}
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};
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int main() {
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auto r = Solution::combinationSum3(5, 30);
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for (const auto& i : r) {
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for (const auto& j : i) {
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std::cout << j << ' ';
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}
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std::cout << std::endl;
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}
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return 0;
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}
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