leetcode题记——Two Sum II - Input array is sorted

原创于 2018-02-08 15:36:09 发布 · 179 阅读

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本文介绍了一种在已排序的整数数组中寻找两个数使其和等于特定目标值的有效算法。该算法采用双指针技术，从数组两端开始向中间逼近，直到找到满足条件的两个数。这种方法充分利用了数组的有序特性，极大地提高了搜索效率。

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. Please note that 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.

Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2

class Solution {
    public int[] twoSum(int[] numbers, int target) {
        int a[] = new int[2];
        int l = 0, r = numbers.length - 1;
        while (l < r) {
            int sum = numbers[l] + numbers[r];
            if (sum == target) {
                a[0]=l+1;
                a[1]=r+1;
                return a;
            }else if (sum < target) 
                ++l;
            else 
                --r;
        }
        return a;
    }
}