LeetCode刷题【Array】 Two Sum II - Input array is sorted

最新推荐文章于 2018-09-07 17:30:30 发布

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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方法。提供两种解决方案，一种利用哈希表实现快速查找，另一种采用双指针技术在有序数组中高效解决问题。

题目：

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

解决方法一：Runtime: 5 ms

public class Solution {
    public int[] twoSum(int[] numbers, int target) {
        
        Map<Integer,Integer> map = new HashMap<Integer,Integer>();
        int ret[] = new int[2];
        for(int i=0;i<numbers.length;i++){
            if(map.containsKey(target-numbers[i])){
                ret[1]=i+1;
                ret[0]=map.get(target-numbers[i])+1;
                return ret;
            }
            map.put(numbers[i],i);
        }
        return ret;
    }
}

解决方法二：Runtime: 2 ms

public class Solution {
    public int[] twoSum(int[] numbers, int target) {
        int ret[] = new int[2];
        int start=0;int end=numbers.length-1;
        while(start<end){
            if(numbers[start]+numbers[end]==target){
                ret[0]=start+1;
                ret[1]=end+1;
                break;
            }
            if(numbers[start]+numbers[end]>target){
                end--;
            }else if(numbers[start]+numbers[end]<target){
                start++;
            }
        }
        return ret;
    }
}

参考：

【1】https://leetcode.com/