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Missing Number

Leetcode

Given an array nums containing n distinct numbers in the range [0, n], return the only number in the range that is missing from the array.

Example 1: 

Input: nums = [3,0,1]
Output: 2
Explanation: n = 3 since there are 3 numbers, so all numbers are in the range [0,3]. 2 is the missing number in the range since it does not appear in nums.

Solution 1

Solution 1

public int missingNumber(int[] nums) {
  int sum = nums.length;
  for (int i = 0; i < nums.length; i++) {
    sum += i - nums[i] ;
  }
  return sum;
}

Solution 2

Solution 2

public int missingNumber(int[] nums) {
  boolean[] found = new boolean[nums.length + 1];
  for (int i = 0; i < nums.length; i++) {
    found[nums[i]] = true;
  }
 
  for (int i = 0; i < found.length; i++) {
    if (!found[i]) {
      return i;
    }
  }
  return -1;
}