Missing Ranges

Source

• leetcode: 163

Given a sorted integer array where the range of elements are [0, 99]
inclusive, return its missing ranges.
For example, given [0, 1, 3, 50, 75], return [“2”, “4->49”, “51->74”,
“76->99”]

Java

public List<String> findMissingRanges(int[] a, int lo, int hi) {
  List<String> res = new ArrayList<String>();

  // the next number we need to find
  int next = lo;

  for (int i = 0; i < a.length; i++) {
    // not within the range yet
    if (a[i] < next) continue;

    // continue to find the next one
    if (a[i] == next) {
      next++;
      continue;
    }

    // get the missing range string format
    res.add(getRange(next, a[i] - 1));

    // now we need to find the next number
    next = a[i] + 1;
  }

  // do a final check
  if (next <= hi) res.add(getRange(next, hi));

  return res;
}

String getRange(int n1, int n2) {
  return (n1 == n2) ? String.valueOf(n1) : String.format("%d->%d", n1, n2);
}