78. 子集

递归

class Solution {
	private List ls; 
	private boolean []bool;
	private int n;
	public List<List<Integer>> subsets(int[] nums) {
		n = nums.length;
		ls = new LinkedList<LinkedList>();
        if(n==0)return ls;
		bool = new boolean [n];
        dfs(nums,0,bool);
		return ls;
	}
	public void dfs(int nums[],int u,boolean bool[]) {
		if(u==n) {
			LinkedList path = new LinkedList<LinkedList>();
			for(int i = 0 ; i< n ;i++) {
				if(bool[i]==false)
					path.add(nums[i]);
			}
			ls.add(path);
		}
		else {
			bool[u]= true;
            dfs( nums,u+1,bool);
            bool[u] = false;
            dfs( nums,u+1,bool);
		}
	}

}

回溯+二进制

class Solution {
	private List ls;
	private boolean[] bool;
	private int n;

	public List<List<Integer>> subsets(int[] nums) {
		n = nums.length;
		ls = new LinkedList<LinkedList>();
		bool = new boolean[n];
		for (int i = 0; i < Math.pow(2, n); i++) {
			LinkedList path = new LinkedList<LinkedList>();
			String s = Integer.toBinaryString(i);
			while(s.length()!=n) s = '0'+s;
			for (int x = 0; x < n; x++)
				if (s.charAt(x) == '1')
					path.add(nums[x]);
			ls.add(path);
		}
		return ls;
	}
}