combination sum III

Author: zgpeace

code/LeetCode/src/backtracking/CombinationSumIII.java

@@ -0,0 +1,44 @@
+package backtracking;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+// https://leetcode.com/problems/combination-sum-iii/
+public class CombinationSumIII {
+
+  public static void main(String[] args) {
+    int k = 3;
+    int n = 9;
+    CombinationSumIII obj = new CombinationSumIII();
+    List<List<Integer>> resultList = obj.combinationSum3(k ,n);
+    System.out.println(Arrays.toString(resultList.toArray()));
+  }
+
+  public List<List<Integer>> combinationSum3(int k, int n) {
+    List<List<Integer>> resultList = new ArrayList<List<Integer>>();
+    // dfs
+    dfs(resultList, new ArrayList<Integer>(), k, n, 1);
+
+    return resultList;
+  }
+
+  private void dfs(List<List<Integer>> resultList, List<Integer> list, int k, int sum, int start) {
+    if (sum == 0 && k == 0) {
+      resultList.add(new ArrayList<Integer>(list));
+      return;
+    }
+    if (sum < 0 || start > 9) {
+      return;
+    }
+    for (int i = start; i <= 9; i++) {
+      // add num
+      list.add(i);
+      dfs(resultList, list, k - 1, sum - i, i + 1);
+
+      // not add num
+      list.remove(list.size() - 1);
+    }
+  }
+
+}