Data Structures: Hash Tables

// Google Question
// Given an array = [2,5,1,2,3,5,1,2,4]:
// It should return 2

//Given an array = [2,1,1,2,3,5,1,2,4]:
// It should return 1

// Given an array = [2,3,4,5]:
// It should return undefined

function firstRecurringCharacter(input) {
    
    for (let i = 0; i<input.length; i++) {
        for (let j=i+1; j < input.length; j++) {
            if (input[i] === input[j]) {
                return input[i]
            }
        }
    }
    return undefined;
} // O(n^2)


function firstRecurringCharacter2(input) {
    let map = {};
    for (let i = 0; i < input.length; i++) {
        if (map[input[i]] !== undefined) {
            return input[i];
        } else {
            map[input[i]] = i;
        }
    }
    console.log(map);
    return undefined;
}

firstRecurringCharacter2([2,5,1,2,3,5,1,2,4]);