s0027_remove_element.rs

/**
 * [27] Remove Element
 *
 * Given an array nums and a value val, remove all instances of that value <a href="https://en.wikipedia.org/wiki/In-place_algorithm" target="_blank">in-place</a> and return the new length.
 *
 * Do not allocate extra space for another array, you must do this by modifying the input array <a href="https://en.wikipedia.org/wiki/In-place_algorithm" target="_blank">in-place</a> with O(1) extra memory.
 *
 * The order of elements can be changed. It doesn't matter what you leave beyond the new length.
 *
 * Example 1:
 *
 *
 * Given nums = [3,2,2,3], val = 3,
 *
 * Your function should return length = 2, with the first two elements of nums being 2.
 *
 * It doesn't matter what you leave beyond the returned length.
 *
 *
 * Example 2:
 *
 *
 * Given nums = [0,1,2,2,3,0,4,2], val = 2,
 *
 * Your function should return length = 5, with the first five elements of nums containing 0, 1, 3, 0, and 4.
 *
 * Note that the order of those five elements can be arbitrary.
 *
 * It doesn't matter what values are set beyond the returned length.
 *
 * Clarification:
 *
 * Confused why the returned value is an integer but your answer is an array?
 *
 * Note that the input array is passed in by reference, which means modification to the input array will be known to the caller as well.
 *
 * Internally you can think of this:
 *
 *
 * // nums is passed in by reference. (i.e., without making a copy)
 * int len = removeElement(nums, val);
 *
 * // any modification to nums in your function would be known by the caller.
 * // using the length returned by your function, it prints the first len elements.
 * for (int i = 0; i < len; i++) {
 *     print(nums[i]);
 * }
 *
 */
pub struct Solution {}

// problem: https://leetcode.com/problems/remove-element/
// discuss: https://leetcode.com/problems/remove-element/discuss/?currentPage=1&orderBy=most_votes&query=

// submission codes start here

impl Solution {
    pub fn remove_element(nums: &mut Vec<i32>, val: i32) -> i32 {
        if nums.len() < 1 {
            return 0;
        }
        let (mut start, mut end) = (0_usize, nums.len() - 1);
        while start < end {
            if nums[start] == val {
                nums[start] = nums[end - 1];
                end -= 1;
            } else {
                start += 1;
            }
        }
        end as i32
    }
}

// submission codes end

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

    #[test]
    fn test_27() {
        let mut vec1 = vec![0, 1, 2, 2, 3, 0, 4, 2];
        assert_eq!(Solution::remove_element(&mut vec1, 2), 5);
        assert_eq!(vec1[0..5], [0, 1, 4, 0, 3]);
        assert_eq!(Solution::remove_element(&mut vec![], 2), 0);
        assert_eq!(
            Solution::remove_element(&mut vec![1, 2, 2, 2, 2, 2, 2], 2),
            1
        );
        assert_eq!(
            Solution::remove_element(&mut vec![2, 2, 2, 2, 2, 2, 2], 2),
            0
        );
        assert_eq!(Solution::remove_element(&mut vec![1], 1), 0);
    }
}