factor combinations

Author: zgpeace

code/LeetCode/src/backtracking/FactorCombinations.java

@@ -0,0 +1,59 @@
+package backtracking;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+// https://leetcode.com/problems/factor-combinations/
+public class FactorCombinations {
+
+  public static void main(String[] args) {
+    FactorCombinations obj = new FactorCombinations();
+    int n = 12;
+    List<List<Integer>> resultList = obj.getFactors(12);
+    System.out.println(Arrays.toString(resultList.toArray()));
+  }
+
+  public List<List<Integer>> getFactors(int n) {
+    List<List<Integer>> resultList = new ArrayList<List<Integer>>();
+    // DFS
+    //dfs(resultList, new ArrayList<Integer>(), n, 2);
+    dfs1(resultList, new ArrayList<Integer>(), n, 2);
+
+    return resultList;
+  }
+
+  private void dfs(List<List<Integer>> resultList, List<Integer> list, int n, int start) {
+    // exit
+    if (n == 1) {
+      if (list.size() > 1) {
+        resultList.add(new ArrayList<Integer>(list));
+      }
+
+      return;
+    }
+
+    for (int i = start; i <= n; i++) {
+      if (n % i == 0) {
+        list.add(i);
+        dfs(resultList, list, n / i, i);
+
+        list.remove(list.size() - 1);
+      }
+    }
+  }
+
+
+  private void dfs1(List<List<Integer>> resultList, List<Integer> list, int n, int start) {
+    for (int i = start; i * i < n; i++) {
+      if (n % i == 0) {
+        List<Integer> newList = new ArrayList<Integer>(list);
+        newList.add(i);
+        dfs1(resultList, newList, n / i, i);
+
+        newList.add(n / i);
+        resultList.add(new ArrayList<Integer>(newList));
+      }
+    }
+  }
+}