LeetCode 1 找出两个数之和



Given an array of integers, 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.

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

利用字典的查找优势,遍历一次输入,如果字典中存在target - nums[i]则结束,否则添加到字典.

c#

public class Solution {
    public int[] TwoSum(int[] nums, int target)
    {
        int[] index=new int[2];
        Dictionary<int,int> dict=new Dictionary<int,int>();
        for(int i=0;i<nums.Length;i++)
        {
           if(dict.Keys.Contains(target-nums[i]))
           {
               index[0]=dict[target-nums[i]]+1;
               index[1]=i+1;
               break;
           }
           else
           {
               if(!dict.Keys.Contains(nums[i]))
               dict.Add(nums[i],i);
           }
        }
        return index;
    }
}