Basic easy level programs

Basic Programs:
1.Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

Solution:

public int[] twoSum(int[] nums, int target) {
    Map<Integer, Integer> map = new HashMap<>();
    for (int i = 0; i < nums.length; i++) {
        int complement = target - nums[i];
        if (map.containsKey(complement)) {
            return new int[] { map.get(complement), i };
        }
        map.put(nums[i], i);
    }
    throw new IllegalArgumentException("No two sum solution");
}

2. Given an unsorted integer array, find the first missing positive integer.

For example,
Given [1,2,0] return 3,
and [3,4,-1,1] return 2.

Your algorithm should run in O(n) time

Solution:

    public int firstMissingPositive(int[] nums) {

     Map<Integer, Integer> map=new HashMap<>();

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

   map.put(i,nums[i]);

int num = 0,x=0;

for(int i=1;i<Integer.MAX_VALUE;i++)

  {

     if(!map.containsValue(i))

    { num=i;

                                break;}

    }return num;  }