If we can assume that the sum total of all of the values in the array with the missing value is equal to the sum of all of the values of a full array minus the missing values couldn’t we take this approach? this would be time complexity O(n) and space complexity O(1). Am I missing something?
const find_missing_number = function(nums) {
let partial = 0;
let full = 0;
for (let i = 0; i < nums.length; i++) {
partial += nums[i];
full += i;
if (i + 1 === nums.length) full += (i + 1);
}
if (partial === full) return -1;
return full - partial;
};