78. 子集
class Solution {
public List<List<Integer>> subsets(int[] nums) { List<Integer> path = new ArrayList<>(); List<List<Integer>> res = new ArrayList<>(); dfs(nums, path, res, 0); return res; } private void dfs(int[] nums, List<Integer> path, List<List<Integer>> res, int start) { res.add(new ArrayList<Integer>(path)); for(int i = start; i < nums.length; i ++) { path.add(nums[i]); dfs(nums, path, res, i+1); path.remove(path.size() - 1); } }}
470. 用Rand7（）实现Rand10（）
class Solution extends SolBase {
public int rand10() {
int ans = 0;
do {
int x = rand7();
int y = rand7();
ans = (x - 1) * 7 + (y - 1);
} while (ans >= 40);
return 1 + ans % 10;
}
}
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