n0090_subsets_ii.rs

/**
 * [90] Subsets II
 *
 * Given a collection of integers that might contain duplicates, nums, return all possible subsets (the power set).
 *
 * Note: The solution set must not contain duplicate subsets.
 *
 * Example:
 *
 *
 * Input: [1,2,2]
 * Output:
 * [
 *   [2],
 *   [1],
 *   [1,2,2],
 *   [2,2],
 *   [1,2],
 *   []
 * ]
 *
 *
 */
pub struct Solution {}

// submission codes start here

/*
count the repeats of each number,
then in backtracking, each number can be picked up for 0..repeat times

using BTreeMap to preserve order (easy for test)
*/
use std::collections::BTreeMap;
impl Solution {
    pub fn subsets_with_dup(nums: Vec<i32>) -> Vec<Vec<i32>> {
        let mut res = Vec::new();
        let nums = nums
            .into_iter()
            .fold(BTreeMap::new(), |mut map, v| {
                *map.entry(v).or_insert(0) += 1;
                map
            })
            .into_iter()
            .collect::<Vec<(i32, i32)>>();
        Solution::backtrack(0, vec![], &nums, &mut res);
        res
    }

    fn backtrack(
        start: usize,
        mut curr: Vec<i32>,
        nums: &Vec<(i32, i32)>,
        result: &mut Vec<Vec<i32>>,
    ) {
        if start >= nums.len() {
            result.push(curr);
            return;
        }
        for repeat in 0..nums[start].1 + 1 {
            let mut inner = curr.clone();
            for _ in 0..repeat {
                inner.push(nums[start].0);
            }
            Solution::backtrack(start + 1, inner, nums, result);
        }
    }
}

// submission codes end

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_90() {
        assert_eq!(
            Solution::subsets_with_dup(vec![1, 2, 2]),
            vec![
                vec![],
                vec![2],
                vec![2, 2],
                vec![1],
                vec![1, 2],
                vec![1, 2, 2],
            ]
        );
        assert_eq!(Solution::subsets_with_dup(vec![1]), vec![vec![], vec![1],]);
        assert_eq!(Solution::subsets_with_dup(vec![]), vec![vec![],]);
    }
}