LeetCode0041.java

/* First Missing Positive
 * Input: nums = [3,4,-1,1]
 * Output: 2
 * */

public class LeetCode0041 {
    public static void main(String args[]) {
        int[] nums = {3, 4, -1, 1};
        System.out.println(firstMissingPositive(nums));
    }

    public static int firstMissingPositive(int[] nums) {
        if (nums == null || nums.length == 0)
            return 1;

        for (int i = 0; i < nums.length; i++) {
            while (nums[i] > 0 && nums[i] <= nums.length && nums[i] != nums[nums[i] - 1]){
                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;
    }
}