int findElementThatAppearsOnce(List<int>arr) {
var size = arr.length;
var element = arr[0];
for (var i = 1; i < size; i++) {
element = element ^ arr[i];
}
return element;
}
void main() {
List<int> arr = [7, 2, 2, 4, 5, 8, 3, 4, 5, 7, 8];
print(findElementThatAppearsOnce(arr));
}
/*
run:
3
*/