【LeetCode算法练习（C++）】First Missing Positive

题目：
Given an unsorted integer array, find the first missing positive integer.
For example,
Given [1,2,0] return 3,
and [3,4,-1,1] return 2.
Your algorithm should run in O(n) time and uses constant space.

链接：First Missing Positive

解法：打表，将出现的正数在表中置0，遍历列表返回第一个非0的序号。时间O(n)

class Solution {
public:
    int firstMissingPositive(vector<int>& nums) {
        vector<int> tmp;
        int len = nums.size();
        if (len == 0) return 1;

        for (int i = 0; i <= len; i++) {
            tmp.push_back(i);
        }
        for (int i = 0; i < len; i++) {
            if (nums[i] > 0 && nums[i] <= len) tmp[nums[i]] = 0;
        }
        for (int i = 0; i <= len; i++) {
            if (tmp[i]) return i;
        }
        return len + 1;
    }
};

Runtime: 3 ms