041.md

41. First Missing Positive

Solution 1 (O(n))

class Solution {
    public int firstMissingPositive(int[] nums) {
        if (nums.length == 0)
            return 1;
        for (int i = 0; i < nums.length; i++) {
            while (nums[i] > 0 && nums[i] <= nums.length
                   && nums[nums[i] - 1] != nums[i]) {
                int temp = nums[nums[i] - 1];
                nums[nums[i] - 1] = nums[i];
                nums[i] = temp;
            }
        }
        for (int i = 0; i < nums.length; i++) {
            if (nums[i] != i + 1) {
                return i + 1;
            }
        }
        return nums.length + 1;
    }
}