唉，上周末立的flag：我就要废了 这周总算有了一个开始。
题目：给出一个整数数组，返回两个数的下标值，令其和等于一个指定的目标值
代码语言：javascript复制Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] nums[1] = 2 7 = 9,
return [0, 1].hash实现：
代码语言：javascript复制 #include <iostream>
using namespace std;
#include <unordered_map>
#include <vector>
int main()
{
vector<int> nums{2,7,11,15};
int target = 9;
vector<int> ans;
unordered_map<int,int> hashmap;
for(int i=0;i<nums.size();i )
{
if(hashmap[target-nums[i]] && hashmap[target-nums[i]] != i 1)
{
//防止利用同个元素
ans.push_back(hashmap[target-nums[i]]-1);//它的下标更小，放在前面
ans.push_back(i);
}
//将hash表对应下标 1,防止处理下标为0的情况
hashmap[nums[i]]=i 1;
}
for(int i=0; i<ans.size();i )
cout<<ans[i]<<endl;
}补充hash:
来源https://blog.csdn.net/summer00072/article/details/80762935
代码语言：javascript复制#include <iostream>
#include <string>
#include <unordered_map>
// reference: http://www.cplusplus.com/reference/unordered_map/unordered_map/at/
typedef std::unordered_map<std::string, std::string> stringmap;
// 将 a, b 融合为一个 unordered_map
stringmap merge(stringmap a, stringmap b) {
// unordered_map 复制构造函数
stringmap temp(a);
// 范围插入，将 b 全部插入进 a 中
temp.insert(b.begin(), b.end());
return temp;
}
int main()
{
//============================
// 1. unordered_map 元素计算与基础遍历
//============================
// 定义第一个 unordered_map
std::unordered_map<std::string, int> mymap = { { "Mars", 3000 }, { "Saturn", 60000 }, { "Jupiter", 70000 } };
// 对元素进行计算
mymap.at("Mars") = 3396;
mymap.at("Saturn") = 272;
mymap.at("Jupiter") = mymap.at("Saturn") 9638;
// auto：自动判断类型
// 基于范围的 for 循环，遍历 mymap
for (auto& x : mymap) {
std::cout << x.first << ": " << x.second << std::endl;
}
std::cout << "mymap.size() is " << mymap.size() << std::endl << std::endl;
//============================
// 2. iterator, 迭代器遍历
//============================
// 定义第二个 unordered_map
std::unordered_map<std::string, std::string> mymap2 = { { "Australia", "Canberra" }, { "U.S.", "Washington" }, { "France", "Paris" } };
std::cout << "mymap2 contains:" << std::endl;
// 遍历 mymap2
for (auto it = mymap2.begin(); it != mymap2.end(); it)
std::cout << " " << it->first << ":" << it->second << std::endl;
std::cout << std::endl;
// mymap2 分配的各桶中的元素
std::cout << "mymap2's buckets contain:n";
for (unsigned i = 0; i < mymap2.bucket_count(); i) {
std::cout << "bucket #" << i << " contains:";
for (auto local_it = mymap2.begin(i); local_it != mymap2.end(i); local_it)
std::cout << " " << local_it->first << ":" << local_it->second;
std::cout << std::endl;
}
//============================
// 3. bucker, 桶操作
//============================
// 定义第三个 unordered_map
std::unordered_map<std::string, std::string> mymap3 = {
{ "us", "United States" },
{ "uk", "United Kingdom" },
{ "fr", "France" },
{ "de", "Germany" }
};
// 遍历 mymap3
for (auto& x : mymap3) {
std::cout << "Element [" << x.first << ":" << x.second << "]";
// 返回元素所在桶号
std::cout << " is in bucket #" << mymap3.bucket(x.first) << std::endl;
}
//============================
// 4. count ，判断元素是否在容器中
//============================
// 定义第四个 unordered_map
std::unordered_map<std::string, double> mymap4 = {
{ "Burger", 2.99 },
{ "Fries", 1.99 },
{ "Soda", 1.50 } };
// 遍历 mymap4
for (auto& x : { "Burger", "Pizza", "Salad", "Soda" })
{
// 判断 x 是否在容器中
if (mymap4.count(x)>0)
std::cout << "mymap4 has " << x << std::endl;
else
std::cout << "mymap4 has no " << x << std::endl;
}
//============================
// 5. erase ，删除操作
//============================
// 定义第五个 unordered_map
std::unordered_map<std::string, std::string> mymap5;
mymap5["U.S."] = "Washington";
mymap5["U.K."] = "London";
mymap5["France"] = "Paris";
mymap5["Russia"] = "Moscow";
mymap5["China"] = "Beijing";
mymap5["Germany"] = "Berlin";
mymap5["Japan"] = "Tokyo";
// 通过迭代器删除
mymap5.erase(mymap5.begin());
// 通过 Key 值删除
mymap5.erase("France");
// 通过迭代器范围删除
mymap5.erase(mymap5.find("China"), mymap5.end());
// 基于范围的 for 循环，遍历展示删除后的 mymap
for (auto& x : mymap5)
std::cout << x.first << ": " << x.second << std::endl;
//============================
// 6. find ，搜索操作
//============================
// 定义第六个 unordered_map
std::unordered_map<std::string, double> mymap6 = {
{ "mom", 5.4 },
{ "dad", 6.1 },
{ "bro", 5.9 } };
std::string input;
std::cout << "who? ";
// 输入 mom, dad, bro 中的一个，否则搜索失败返回 Not Found
getline(std::cin, input);
// 根据输入参数 Key 值进行搜索，返回一个迭代器
std::unordered_map<std::string, double>::const_iterator got = mymap6.find(input);
// find 返回值若为 unordered_map 的尾部，则没有在容器中找到
if (got == mymap6.end())
std::cout << "not found";
else
std::cout << got->first << " is " << got->second;
std::cout << std::endl;
//============================
// 6. insert ，插入操作
//============================
// 定义第七、八个 unordered_map
std::unordered_map<std::string, double>
myrecipe,
mypantry = { { "milk", 2.0 }, { "flour", 1.5 } };
// 定义插入元素，类型为 pair 的对象
std::pair<std::string, double> myshopping("baking powder", 0.3);
// 复制插入
myrecipe.insert(myshopping);
// 移动插入
myrecipe.insert(std::make_pair<std::string, double>("eggs", 6.0));
// 范围插入
myrecipe.insert(mypantry.begin(), mypantry.end()); // range insertion
// 初始化列表插入
myrecipe.insert({ { "sugar", 0.8 }, { "salt", 0.1 } }); // initializer list insertion
std::cout << "myrecipe contains:" << std::endl;
for (auto& x : myrecipe)
std::cout << x.first << ": " << x.second << std::endl;
std::cout << std::endl;
//============================
// 7. 等于运算符 = 操作
//============================
// 初始化列表
stringmap first = { { "AAPL", "Apple" }, { "MSFT", "Microsoft" } };
stringmap second = { { "GOOG", "Google" }, { "ORCL", "Oracle" } };
// 移动
stringmap third = merge(first, second);
// 复制
first = third;
std::cout << "first contains:";
for (auto& elem : first) std::cout << " " << elem.first << ":" << elem.second;
std::cout << std::endl;
return 0;
}
