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Day-11 Subsets
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Day-11 Subsets
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//Cascading
class Solution {
public List<List<Integer>> subsets(int[] nums) {
List<List<Integer>> output = new ArrayList();
output.add(new ArrayList<Integer>());
for (int num : nums) {
List<List<Integer>> newSubsets = new ArrayList();
for (List<Integer> curr : output) {
newSubsets.add(new ArrayList<Integer>(curr){{add(num);}});
}
for (List<Integer> curr : newSubsets) {
output.add(curr);
}
}
return output;
}
}
//Backtracking
class Solution {
List<List<Integer>> output = new ArrayList();
int n, k;
public void backtrack(int first, ArrayList<Integer> curr, int[] nums) {
// if the combination is done
if (curr.size() == k)
output.add(new ArrayList(curr));
for (int i = first; i < n; ++i) {
// add i into the current combination
curr.add(nums[i]);
// use next integers to complete the combination
backtrack(i + 1, curr, nums);
// backtrack
curr.remove(curr.size() - 1);
}
}
public List<List<Integer>> subsets(int[] nums) {
n = nums.length;
for (k = 0; k < n + 1; ++k) {
backtrack(0, new ArrayList<Integer>(), nums);
}
return output;
}
}
//Lexographic
class Solution {
public List<List<Integer>> subsets(int[] nums) {
List<List<Integer>> output = new ArrayList();
int n = nums.length;
for (int i = (int)Math.pow(2, n); i < (int)Math.pow(2, n + 1); ++i) {
// generate bitmask, from 0..00 to 1..11
String bitmask = Integer.toBinaryString(i).substring(1);
// append subset corresponding to that bitmask
List<Integer> curr = new ArrayList();
for (int j = 0; j < n; ++j) {
if (bitmask.charAt(j) == '1') curr.add(nums[j]);
}
output.add(curr);
}
return output;
}
}