Array&String - Two Sum.md

Question:

Given an array of integers, find two numbers such that they add up to a specific target number.
Return two indices, where index1 must be less than index2 and they are not zero-based (this means that the index start from 1 not 0).
Assume there is only one solution.

Solution in Java:

public int[] twoSum(int[] numbers, int target) {
  Map<Integer, Integer> map = new HashMap<>();
  for(int i = 0; i < numbers.length - 1; i++) {
    int x = numbers[i];
    if(map.containsKey(target - x)) { // when get to this stage, means that another value with a small index already been stored in the map, so the bigger index now is i
      return new int[] {map.get(target - x) + 1, i + 1}; // map.get returns the value to which the specified key is mapped
    }
    map.put(x, i); // put the number x and its index i into the map, (key, value) = (x, i)
  }
  throw new IllegalArgumentException("No two sum solution");
}

Question:

If the input array is sorted in ascending order?

Solution:

public int[] twoSum(int[] numbers, int target) {
  int i = 0, j = numbers.length - 1;
  while(i < j) {
    int sum = numbers[i] + numbers[j];
    if(sum < target) {
      i++ ;
    } else if (sum > target) {
      j-- ;
    } else {
      return new int[] {i + 1, j + 1};
    }
  }
  throw new IllegalArgumentException("No two sum solution");
}

Question:

Design the data structure, a twoSum class.

Solution: