LeetCode 78: Subsets

class Solution {
public List<List<Integer>> subsets(int[] nums) {
List<List<Integer>> result = new ArrayList<>();
result.add(new ArrayList<>());

if (nums.length == 0) {
return result;
}

for (int num : nums) {
List<List<Integer>> newResult = new ArrayList<>(result);
for (List<Integer> row : result) {
List<Integer> newRow = new ArrayList<>(row);
newRow.add(num);
newResult.add(newRow);
}
result = newResult;
}
return result;
}
}

class Solution {
public List<List<Integer>> subsets(int[] nums) {
List<List<Integer>> result = new ArrayList<>();

long recorder = 0;
long bound = (1 << nums.length) - 1;
while (recorder <= bound) {
result.add(toNum(recorder++, nums));
}
return result;
}

private List<Integer> toNum(long recorder, int[] nums) {
List<Integer> result = new ArrayList<>();
int i = nums.length - 1;
while (i >= 0) {
if ((recorder & 1L) == 1L) {
result.add(nums[i]);
}
recorder >>= 1;
i--;
}
return result;
}
}

class Solution {
public List<List<Integer>> subsets(int[] nums) {
List<List<Integer>> result = new ArrayList<>();
result.add(new ArrayList<>());
helper(result, 0, new ArrayList<>(), nums);
return result;
}

private void helper(List<List<Integer>> result, int start, List<Integer> current, int[] nums) {
if (start == nums.length) {
return;
}

for (int i = start; i < nums.length; i++) {
current.add(nums[i]);
result.add(new ArrayList<>(current));
helper(result, i + 1, current, nums);
current.remove(current.size() - 1);
}
}
}