s0039

include/s0039_combination_sum.hpp

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+#ifndef S0039_COMBINATION_SUM_HPP
+#define S0039_COMBINATION_SUM_HPP
+
+#include <vector>
+#include <algorithm>
+#include <iterator>
+
+using namespace std;
+
+class Solution {
+ public:
+  vector<vector<int>> combinationSum(vector<int>& candidates, int target);
+};
+
+#endif

src/s0039_combination_sum.cpp

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+#include "s0039_combination_sum.hpp"
+
+#include <vector>
+
+void dfs(vector<int>& candidates, int target, vector<vector<int>>& ans,
+         vector<int>& combine, int idx) {
+  if (idx == candidates.size()) {
+    return;
+  }
+  if (target == 0) {
+    ans.emplace_back(combine);
+    return;
+  }
+  // 直接跳过
+  dfs(candidates, target, ans, combine, idx + 1);
+  // 选择当前数
+  if (target - candidates[idx] >= 0) {
+    combine.emplace_back(candidates[idx]);
+    dfs(candidates, target - candidates[idx], ans, combine, idx);
+    combine.pop_back();
+  }
+}
+
+vector<vector<int>> Solution::combinationSum(vector<int>& candidates,
+                                             int target) {
+  vector<vector<int>> ans;
+  vector<int> combine;
+  dfs(candidates, target, ans, combine, 0);
+  return ans;
+}

tests/s0039_combination_sum.cpp

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+#include "s0039_combination_sum.hpp"
+
+#include <gtest/gtest.h>
+
+TEST(Problem39, Case1) {
+  vector<int> candidates{2, 3, 6, 7};
+  int target{7};
+  vector<vector<int>> o{{7}, {2, 2, 3}};
+  Solution solution;
+  EXPECT_EQ(solution.combinationSum(candidates, target), o);
+}
+
+TEST(Problem39, Case2) {
+  vector<int> candidates{2, 3, 5};
+  int target{8};
+  vector<vector<int>> o{{3, 5}, {2, 3, 3}, {2, 2, 2, 2}};
+  Solution solution;
+  EXPECT_EQ(solution.combinationSum(candidates, target), o);
+}
+
+TEST(Problem39, Case3) {
+  vector<int> candidates{2};
+  int target{1};
+  vector<vector<int>> o{};
+  Solution solution;
+  EXPECT_EQ(solution.combinationSum(candidates, target), o);
+}