LeetCode（41）——First Missing Positive

Given an unsorted integer array, find the smallest missing positive integer.

Example 1:

Input: [1,2,0]
Output: 3

Example 2:

Input: [3,4,-1,1]
Output: 2

Example 3:

Input: [7,8,9,11,12]
Output: 1

Note:

Your algorithm should run in O(n) time and uses constant extra space.

AC：

class Solution {
    public int firstMissingPositive(int[] nums) {
        Arrays.sort(nums);
        if (null == nums || nums.length == 0 || nums[nums.length - 1] <= 0 || nums[0] > 1) {
            return 1;
        }
        
        int i = Arrays.binarySearch(nums, 1);
        if (i < 0) {
            return 1;
        }
        int target = 1;
        i++;
        while (i < nums.length) {
            if (nums[i] != nums[i - 1]) {
                if (nums[i - 1] + 1 == nums[i]) {
                    target++;
                }
                else {
                    break;
                }
            }
            
            i++;
        }
        
        return target + 1;
    }
}