MissingFirstPositveNumber.java

packagearray;

importjava.util.Arrays;

publicclassMissingFirstPositveNumber {

// O(NlogN) time | O(1) space
publicstaticintfindMissingFirst(int[] arr) {
Arrays.sort(arr);
intans = -1;
for (inti = 1; i < arr.length; i++) {
if (arr[i] != arr[i - 1] + 1) {
ans = arr[i - 1] + 1;
break;
 }
 }
returnans;
 }

publicstaticvoidmain(String[] args) {
int[] arr = { 20, 5, 1, 4 };
System.out.println(findMissingFirst(arr));
 }
}