Leetcode167-Two Sum II Input array is sorted-Easy
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.
思路:
two pointers法:i,j 分别指向sorted array的头和尾,如果numbers[i] + numbers[j] < target, 左指针后移,否则有指针左移。当i = j时,则没有找到和为target对应的index。则返回空。
注意:
j = numbers.length - 1; 不要再忘了-1 才是数组最后一位的index!!
代码:
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) { j--; } else { i++; } } return new int[]{}; }