LeetCode-in-All

287. Find the Duplicate Number

Medium

Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive.

There is only one repeated number in nums, return this repeated number.

You must solve the problem without modifying the array nums and uses only constant extra space.

Example 1:

Input: nums = [1,3,4,2,2]

Output: 2

Example 2:

Input: nums = [3,1,3,4,2]

Output: 3

Constraints:

• 1 <= n <= 105
• nums.length == n + 1
• 1 <= nums[i] <= n
• All the integers in nums appear only once except for precisely one integer which appears two or more times.

Follow up:

• How can we prove that at least one duplicate number must exist in nums?
• Can you solve the problem in linear runtime complexity?

Solution

impl Solution {
    pub fn find_duplicate(nums: Vec<i32>) -> i32 {
        let mut arr = vec![0; nums.len() + 1];
        for &num in &nums {
            arr[num as usize] += 1;
            if arr[num as usize] == 2 {
                return num;
            }
        }
        0
    }
}

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