Complete Backtracking-2

PalindromePartitioning.java

@@ -0,0 +1,41 @@
+import java.util.*;
+
+// Backtracking O(n * 2^n) time, O(n) space
+class Solution {
+    List<List<String>> ans;
+    public List<List<String>> partition(String s) {
+        ans = new ArrayList<>();
+        helper(0, s, new ArrayList<>());
+        return ans;
+    }
+
+    private void helper(int idx, String s, List<String> path) {
+        if (idx == s.length()) {
+            ans.add(new ArrayList<>(path));
+            return;
+        }
+
+        for (int i = idx; i < s.length(); i++) {
+            String substring = s.substring(idx, i+1);
+            if (isPalindrome(substring)) {
+                path.add(substring);
+                helper(i+1, s, path);
+                path.remove(path.size()-1);
+            }
+        }
+    }
+
+    private boolean isPalindrome(String s) {
+        int left = 0;
+        int right = s.length()-1;
+
+        while (left < right) {
+            if (s.charAt(left) != s.charAt(right)) {
+                return false;
+            }
+            left++;
+            right--;
+        }
+        return true;
+    }
+}

Subsets.java

@@ -0,0 +1,29 @@
+import java.util.*;
+
+// O(n * 2^n) time, O(n) space
+class Solution {
+    List<List<Integer>> ans;
+
+    public List<List<Integer>> subsets(int[] nums) {
+        ans = new ArrayList<>();
+        helper(0, nums, new ArrayList<>());
+        return ans;
+    }
+
+    private void helper(int idx, int[] nums, List<Integer> path) {
+        if (idx == nums.length) {
+            ans.add(new ArrayList<>(path));
+            return;
+        }
+
+        // choose idx
+        path.add(nums[idx]);
+        helper(idx+1, nums, path);
+
+        //backtrack
+        path.remove(path.size() - 1);
+
+        // dont choose idx
+        helper(idx+1, nums, path);
+    }
+}