挺简单的困难题

class Solution {
public:
    int firstMissingPositive(vector<int>& nums) {
        sort(nums.begin(),nums.end());
        int n=nums.size();
        int i=0;
        bool b=0;
        if(nums[0]>=0) b=1;
        int p=1;
        for(;i<n;i++){
            if(i+1>0&&i+1<nums.size()&&nums[i]<=0&&nums[i+1]>0){
                nums.erase(nums.begin(),nums.begin()+i+1);
                i=0;
                n=nums.size();
                b=1;
            }
            if(b==1&&nums[i]!=p&&nums[i]!=p-1) {return p;}
            else if(b==1&&nums[i]==p) p++;
        }
        return p;
    }
};