_0167_TwoSumII.java

package leetcode;

/**
 * @author      liyazhou1
 * @No          167
 * @problem     Two Sum II - Input array is sorted
 * @level       Easy
 * @desc        两数之和 II - 输入有序数组
 * @tag
 * @date        2020/01/17
 *
 * <pre>
 * 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.
 *
 * </pre>
 */
public class _0167_TwoSumII {

    /**
     * Note
     * Thought
     * Challenge
     * Algorithm
     * 1.
     * 2.
     * 3.
     * Complexity
     * Time,
     * Space,
     */
    private static class 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) {
                    return new int[]{i + 1, j + 1};
                } else if (sum < target) {
                    i++;
                } else {
                    j--;
                }
            }
            return null;
        }
    }
}