Leetcode-41. 缺失的第一个正数

class Solution {
public:
    int firstMissingPositive(vector<int>& nums) {
        int len = nums.size();
        int *num = new int [len+3];
        
        for (int i= 0; i< len+3; i ++)
        {
            num[i] = 0;
        }
        
        for (int i= 0; i< len; i ++)
        {
            int x = nums[i];
            if (x> 0&& x<= len) ++ num[x];
        }
        
        int ans= -1;
        for (int i= 1; i<= len+1; i ++)  /* 若是nums=[1,2,3],则return 4 */
        {
            if (0== num[i]) 
            {
                ans= i;
                break;
            }
        }
        
        delete[] num;
        return ans;
    }
};