leetcode刷题第一日<两数和问题>

开始就用到了c++的哈希表是真的恶心，首先学习一波基础知识

https://blog.csdn.net/u010025211/article/details/46653519

下面放下大佬的代码

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
      vector<int>a;
        a.push_back(-1);
        for(int i=0;i<nums.size();i++)
        {
        for(int j=i+1;j<nums.size();j++)
           if(nums[i]+nums[j]==target)
           {
               a[0]=i;
               a[1]=j;
               return a;
           }
        }
            
    }
};

这里是完整版代码

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
      vector<int>a;
        a.push_back(-1);
        for(int i=0;i<nums.size();i++)
        {
        for(int j=i+1;j<nums.size();j++)
           if(nums[i]+nums[j]==target)
           {
               a[0]=i;
               a[1]=j;
               return a;
           }
        }
            
    }
};

void trimLeftTrailingSpaces(string &input) {
    input.erase(input.begin(), find_if(input.begin(), input.end(), [](int ch) {
        return !isspace(ch);
    }));
}

void trimRightTrailingSpaces(string &input) {
    input.erase(find_if(input.rbegin(), input.rend(), [](int ch) {
        return !isspace(ch);
    }).base(), input.end());
}

vector<int> stringToIntegerVector(string input) {
    vector<int> output;
    trimLeftTrailingSpaces(input);
    trimRightTrailingSpaces(input);
    input = input.substr(1, input.length() - 2);
    stringstream ss;
    ss.str(input);
    string item;
    char delim = ',';
    while (getline(ss, item, delim)) {
        output.push_back(stoi(item));
    }
    return output;
}

int stringToInteger(string input) {
    return stoi(input);
}

string integerVectorToString(vector<int> list, int length = -1) {
    if (length == -1) {
        length = list.size();
    }

    if (length == 0) {
        return "[]";
    }

    string result;
    for(int index = 0; index < length; index++) {
        int number = list[index];
        result += to_string(number) + ", ";
    }
    return "[" + result.substr(0, result.length() - 2) + "]";
}

int main() {
    string line;
    while (getline(cin, line)) {
        vector<int> nums = stringToIntegerVector(line);
        getline(cin, line);
        int target = stringToInteger(line);
        
        vector<int> ret = Solution().twoSum(nums, target);

        string out = integerVectorToString(ret);
        cout << out << endl;
    }
    return 0;
}

这貌似有点高深但是算法复杂度是非常低的，貌似是4msj解决，我们再利用基础的c暴力解决下，

双重循环遍历，代码如下

int* twoSum(int* nums, int numsSize, int target) {
    int *a;
    a=(int *)malloc(2*sizeof(int));
    for(int i=0;i<numsSize-1;i++)
    {
        for(int j=i+1;j<numsSize;j++)
        {
            if((nums[i]+nums[j])==target)
             {
              a[0]=i;
              a[1]=j;
             }
        }
    }
    return a;

但是这个不是最优的，最优算法貌似是采用二分法 代码像这样

int* twoSum(int* nums, int numsSize, int target) {
    int *a;
    a=(int *)malloc(2*sizeof(int));
    int mid=numsSize/2;
    for(int i=0;i<mid;i++)
    {
        for(int j=mid;j<numsSize;j++)
        {
            if((nums[i]+nums[j])==target)
             {
              a[0]=i;
              a[1]=j;
             }
        }
    }
    return a;

最后在用python解决下吧

def twoSum(self, nums, target):
       hashmap={}
       for index, num in enumerate(nums):
            another_num = target - num
            if another_num in hashmap:
                return [hashmap[another_num], index]
            hashmap[num] = index
       return None