First Missing Positive

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.

解题思路：坑爹题，今天上午做题不在状态啊，晚上再也不熬夜了，就这leetcode上的水题也卡我半小时。

class Solution {
public:
    int firstMissingPositive(vector<int>& nums) {
        int size = nums.size();
        if(size == 0) return 1;
        for(int i = 0; i < size; ++i) {
            if(nums[i] == i + 1) continue;
            while(nums[i] > 0 && nums[i] != i + 1 && nums[i]-1 < size && nums[nums[i]-1] != nums[i]) {
                int t = nums[i];
                nums[i] = nums[nums[i]-1];
                nums[t-1] = t;
                cout << nums[i] << " " << nums[nums[i]-1] << endl;
            }
        }
        for(int i = 0; i < size; ++i) {
            if(nums[i] != i + 1) {
                return i + 1;
            }
        }
        return size + 1;
    }
};