s0216

include/s0216_combination_sum_iii.hpp

@@ -0,0 +1,13 @@
+#ifndef S0216_COMBINATION_SUM_III_HPP
+#define S0216_COMBINATION_SUM_III_HPP
+
+#include <vector>
+
+using namespace std;
+
+class S0216 {
+ public:
+  vector<vector<int>> combinationSum3(int k, int n);
+};
+
+#endif

notes/src/combinations.md

@@ -68,3 +68,7 @@ void combineDFS(int n, int k, int begin, vector<int> &path,
   }
 }
 ```
+
+## [216. 组合总和 III](https://leetcode.cn/problems/combination-sum-iii/)
+
+

src/s0216_combination_sum_iii.cpp

@@ -0,0 +1,27 @@
+#include "s0216_combination_sum_iii.hpp"
+
+void combinationSum3DFS(int k, int n, int begin, vector<int> &path, int sum,
+                        vector<vector<int>> &result) {
+  // 终止条件：高度达到上限且总和为 n
+  if (path.size() == k && sum == n) {
+    result.push_back(path);
+    return;
+  }
+
+  // 开始迭代
+  // 当总和 > n 时，剪枝
+  for (int i = begin; i <= 9 && sum + i <= n; ++i) {
+    sum += i;
+    path.push_back(i);
+    combinationSum3DFS(k, n, i + 1, path, sum, result);
+    sum -= i;
+    path.pop_back();
+  }
+}
+
+vector<vector<int>> S0216::combinationSum3(int k, int n) {
+  vector<int> path{};
+  vector<vector<int>> result;
+  combinationSum3DFS(k, n, 1, path, 0, result);
+  return result;
+}