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  • LeetCode:1. Add Two Numbers

    题目:
    LeetCode:1. Add Two Numbers

    描述:

    Given an array of integers, return indices of the two numbers such that they add up to a specific target.
    You may assume that each input would have exactly one solution, and you may not use the same element twice.

    样例:

    Given nums = [2, 7, 11, 15], target = 9,
    Because nums[0] + nums[1] = 2 + 7 = 9,
    return [0, 1].
    

    分析:

    • 思路如下:
      1) 利用hashmap来存储数组元素以及其对应索引值,提高检索效率
      2) 通过nTarget - vecNum[i]来获取对应的检索目标元素
      3) 返回满足条件的索引值

    代码:

    vector<int> twoSum(vector<int>& vecNum, int nTarget) {
        vector<int> vecTemp;
        unordered_map<int, int> hashMapTemp;
    
        for (int i = 0; i < vecNum.size(); i++)
        {
            hashMapTemp[vecNum[i]] = i;
        }
    
        for (int i = 0; i < vecNum.size(); i++)
        {
            const int nPart = nTarget - vecNum[i];
            if (hashMapTemp.find(nPart) != hashMapTemp.end() && hashMapTemp[nPart] > i)
            {
                vecTemp.push_back(i);
                vecTemp.push_back(hashMapTemp[nPart]);
                break;
            }
        }
    
        return vecTemp;
        }
    

    备注:
    LC上大神的 0ms 的代码:

    vector<int> twoSum(vector<int> &numbers, int target)
    {
        //Key is the number and value is its index in the vector.
    	unordered_map<int, int> hash;
    	vector<int> result;
    	for (int i = 0; i < numbers.size(); i++) {
    		int numberToFind = target - numbers[i];
    
                //if numberToFind is found in map, return them
    		if (hash.find(numberToFind) != hash.end()) {
                        //+1 because indices are NOT zero based
    			result.push_back(hash[numberToFind] + 1);
    			result.push_back(i + 1);			
    			return result;
    		}
    
                //number was not found. Put it in the map.
    		hash[numbers[i]] = i;
    	}
    	return result;
    }
    
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  • 原文地址:https://www.cnblogs.com/liuwfuang96/p/6838919.html
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