int firstMissingPositive(vector& nums) {
sort(nums.begin(),nums.end());
for(int i=0;i<nums.size();i++){
if(nums[i]>=0){
if(nums[i]+1!=nums[i+1]){
return nums[i]+1;
}
}
}

return nums.back()+1;

}

this is my code .

for input [7,8,9,11,12] my code is showing ans 10 , but in your solution it is showing 1.