README.md

448. Find All Numbers Disappeared in an Array

Given an array of integers where 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.

Find all the elements of [1, n] inclusive that do not appear in this array.

Could you do it without extra space and in O(n) runtime? You may assume the returned list does not count as extra space.

Example:

Input:
[4,3,2,7,8,2,3,1]
Output:
[5,6]

Solutions (Rust)

1. Swap Positions

impl Solution {
    pub fn find_disappeared_numbers(nums: Vec<i32>) -> Vec<i32> {
        let mut nums = nums;
        let mut ret = Vec::new();

        for i in 0..nums.len() {
            let mut curr = nums[i];

            while nums[curr as usize - 1] != curr {
                let next = nums[curr as usize - 1];
                nums[curr as usize - 1] = curr;
                curr = next;
            }
        }

        for i in 0..nums.len() {
            if i + 1 != nums[i] as usize {
                ret.push(i as i32 + 1);
            }
        }

        ret
    }
}

2. Mark Positions

impl Solution {
    pub fn find_disappeared_numbers(nums: Vec<i32>) -> Vec<i32> {
        let mut nums = nums;
        let mut ret = Vec::new();

        for i in 0..nums.len() {
            let j = nums[i].abs() as usize - 1;
            nums[j] = -nums[j].abs();
        }

        for i in 0..nums.len() {
            if nums[i] > 0 {
                ret.push(i as i32 + 1);
            }
        }

        ret
    }
}