Java Array, Finding Duplicates

Java Array, Finding Duplicates

I have an array, and am looking for duplicates.

duplicates = false;
for(j = 0; j < zipcodeList.length; j++){
    for(k = 0; k < zipcodeList.length; k++){
        if (zipcodeList[k] == zipcodeList[j]){
            duplicates = true;
        }
    }
}

However, this code doesnt work when there are no duplicates. Whys that?

6

16 Answers

On the nose answer..

duplicates=false;
for (j=0;j<zipcodeList.length;j++)
  for (k=j+1;k<zipcodeList.length;k++)
    if (k!=j && zipcodeList[k] == zipcodeList[j])
      duplicates=true;

Edited to switch .equals() back to == since I read somewhere you're using int, which wasn't clear in the initial question. Also to set k=j+1, to halve execution time, but it's still O(n2).

Maya Lin-Takahashi
Author

Maya Lin-Takahashi

Maya is a hardware enthusiast who tests and reviews smart home devices, smartphones, wearables, and audio gear. She focuses on practical consumer value and build quality.