41. First Missing Positive

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# 題目敘述

Given an unsorted integer array nums . Return the smallest positive integer that is not present in nums .

You must implement an algorithm that runs in O(n) time and uses O(1) auxiliary space.

# Example 1

Input: nums = [1,2,0]
Output: 3
Explanation: The numbers in the range [1,2] are all in the array.

# Example 2

Input: nums = [3,4,-1,1]
Output: 2
Explanation: 1 is in the array but 2 is missing.

# Example 3

Input: nums = [7,8,9,11,12]
Output: 1
Explanation: The smallest positive integer 1 is missing.

# 解題思路

# Solution

import java.util.Arrays;

class Solution {

    public int firstMissingPositive(int[] nums) {

        Arrays.sort(nums);

        int tmp = 1;

        for(int i = 0; i < nums.length; i++){

            if(nums[i] == tmp){

                tmp++;

            }else if(nums[i] > tmp){

                return tmp;

            }

        }

        return tmp;

    }

}