LeetCode146|缺失的第一个正数

示例 1:

输入: [1,2,0]
输出: 3
示例 2:

输入: [3,4,-1,1]
输出: 2
示例 3:

输入: [7,8,9,11,12]
输出: 1
 
 

import java.util.Arrays;
import java.util.HashSet;
import java.util.stream.Collectors;

public class FirstMissingPositiveTest2 {
    public static void main(String[] args) {
        int [] nums={1,2,0};
        firstMissingPositive(nums);
    }

    public static  int firstMissingPositive(int[] nums) {
        if (nums == null || nums.length == 0) {
            return 1;
        }
        int length = nums.length;
        HashSet<Integer> hashSet = Arrays
                .stream(nums)
                .boxed()
                .collect(Collectors.toCollection(() -> new HashSet<>(length)));
        for (int i = 1; i <= nums.length; i++) {
            if (!hashSet.contains(i)) {
                return i;
            }
        }
        return length + 1;
    }
    
}