const findElementThatAppearsOnceInArray = (arr) => {
const map = new Map();
for (const x of arr) {
map.set(x, (map.get(x) || 0) + 1);
}
for (const [key, value] of map) {
if (value === 1) {
return key;
}
}
return -1;
};
const arr = [3, 6, 6, 2, 7, 3, 2, 8, 9, 8, 3, 2, 7, 8];
console.log(findElementThatAppearsOnceInArray(arr));
/*
run:
9
*/