class Solution {
public:
int duplicateInArray(vector<int>& nums) {
int n = nums.size();
bool st[n] = {0};
for (int i = 0; i < n; i ++ )
if (nums[i] > n - 1)
return -1;
bool ok = true;
for (int i = 0; i < n; i ++ )
{
if (st[nums[i]]) return nums[i];
st[nums[i]] = true;
}
return -1;
}
};