Largest Unique Number
Description
Given an integer array nums, return the largest integer that only occurs once. If no integer occurs once, return -1.
Example 1:
Input: nums = [5,7,3,9,4,9,8,3,1]
Output: 8
Explanation: The numbers that occur once are [5,7,4,8,1]. The largest of these is 8.
Example 2:
Input: nums = [9,9,8,8]
Output: -1
Explanation: All numbers appear twice, so there is no unique number.
Example 3:
Input: nums = [5]
Output: 5
Explanation: 5 is the only number and it occurs once, so it is the largest unique number.
Constraints
1 <= nums.length <= 20000 <= nums[i] <= 1000
Complexity
Show Complexity
- Time:
O(n) - Space:
O(n)
Hints
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- Pattern
- Hash map counting
- Approach
- Use Counter or dict to count frequencies, iterate to find largest with frequency 1
- Complexity
- Count occurrences, then find max with count = 1
Solutions
Show PY Solution
from collections import defaultdict
def solution(nums: list[int]) -> int:
m = defaultdict(int)
for v in nums:
m[v] += 1
largest = -1
for k, v in m.items():
if v == 1:
largest = max(largest, k)
return largest