how to retrun the number in an array that only appears once in python code example

Example 1: Given an array of integers, every element appears thrice except for one which occurs once.

// declaring an array double[] data; // allocating memory data = new Double[5];

Example 2: Given an array of integers, every element appears thrice except for one which occurs once.

let contacts = new Map()
contacts.set('Jessie', {phone: "213-555-1234", address: "123 N 1st Ave"})
contacts.has('Jessie') // true
contacts.get('Hilary') // undefined
contacts.set('Hilary', {phone: "617-555-4321", address: "321 S 2nd St"})
contacts.get('Jessie') // {phone: "213-555-1234", address: "123 N 1st Ave"}
contacts.delete('Raymond') // false
contacts.delete('Jessie') // true
console.log(contacts.size) // 1