First unique number in list
Java
Medium
7 views
Problem Description
Task: return the first number that appears exactly once in the list, else return null.
Output Format
Return value
Constraints
Preserve insertion order using LinkedHashMap.
Official Solution
static Integer firstUnique(java.util.List<Integer> list){java.util.LinkedHashMap<Integer,Integer> m=new java.util.LinkedHashMap<>();for(Integer x:list) m.put(x,m.getOrDefault(x,0)+1);for(java.util.Map.Entry<Integer,Integer> e:m.entrySet()) if(e.getValue()==1) return e.getKey();return null;}
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