Find First Duplicate Value in Large Array
function findDuplicate(arr) {
const a = new Set();
for (const n of arr) {
if (a.has(n)) return n;
else a.add(n);
}
return -1;
}
function findDuplicate(arr) {
const a = new Set();
for (const n of arr) {
if (a.has(n)) return n;
else a.add(n);
}
return -1;
}