TwoSumII_InputArrayIsSorted.java

package easy._167;

/**
 * @author Larry
 *
 * Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number.
 *
 * The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2.
 *
 * Note:
 *
 * Your returned answers (both index1 and index2) are not zero-based.
 * You may assume that each input would have exactly one solution and you may not use the same element twice.
 * Example:
 *
 * Input: numbers = [2,7,11,15], target = 9
 * Output: [1,2]
 * Explanation: The sum of 2 and 7 is 9. Therefore index1 = 1, index2 = 2.
 */

public class TwoSumII_InputArrayIsSorted {

    public int[] twoSum(int[] numbers, int target) {

        int index1 = 0;
        int index2 = numbers.length - 1;

        while (index1 < index2) {
            int tmp = numbers[index1] + numbers[index2];
            if (tmp < target) index1 ++;
            else if (tmp > target) index2 --;
            else return new int[] { index1 + 1, index2 + 1 };
        }

        return null;

    }

}