學(xué) C++ 沖著打比賽應(yīng)從以下幾點(diǎn)入手:1. 熟練基礎(chǔ)語法但不必深入,掌握變量定義、循環(huán)、條件判斷、函數(shù)等基本內(nèi)容;2. 重點(diǎn)掌握 STL 容器如 vector、map、set、queue、stack 的使用;3. 學(xué)會快速輸入輸出技巧,如關(guān)閉同步流或使用 scanf 和 printf;4. 利用模板與宏簡化代碼書寫,提高效率;5. 多刷題熟悉邊界條件、初始化錯(cuò)誤等常見細(xì)節(jié)問題。
學(xué) C++ 應(yīng)該從哪些地方入手?如果你是沖著打比賽來的,那重點(diǎn)就不只是語法了,得掌握怎么快速寫代碼、用好 STL、還有熟悉一些常用的技巧。下面這些內(nèi)容都是在刷題和比賽中會頻繁用到的。

基礎(chǔ)語法要熟練但不必深入
你不需要把整個(gè) C++ 語言都吃透,但基本的變量定義、循環(huán)、條件判斷、函數(shù)這些必須熟練。比如 for
循環(huán)怎么寫、數(shù)組怎么初始化、引用和指針的區(qū)別等等。

常見的幾個(gè)注意點(diǎn):
-
int main()
是程序入口,別寫成void main()
。 -
cin
和cout
是輸入輸出的主要方式,雖然慢一點(diǎn),但在多數(shù)情況下夠用了。 - 多用
using namespace std;
可以省事,雖然不是最佳實(shí)踐,但在比賽中可以接受。
舉個(gè)例子:

#include <iostream> using namespace std; int main() { int n; cin >> n; for(int i = 0; i < n; ++i) { cout << i << " "; } }
熟練使用 STL 容器是關(guān)鍵
C++ 的優(yōu)勢之一就是標(biāo)準(zhǔn)庫(STL)強(qiáng)大。比賽中最常用的是這幾個(gè)容器:
vector
:動態(tài)數(shù)組,非常靈活map
/unordered_map
:用來做鍵值對查找set
/unordered_set
:用于快速查重或排序queue
/stack
:配合 BFS 或 DFS 使用
舉個(gè)例子,你想統(tǒng)計(jì)某個(gè)數(shù)組中每個(gè)數(shù)字出現(xiàn)的次數(shù),用 map<int, int>
就很方便:
map<int, int> count; for(int num : nums) { count[num]++; }
建議:
- 不要死記復(fù)雜度,但要知道哪個(gè)操作是 O(1),哪個(gè)是 O(log n)
- 多用
auto
簡化代碼,比如for(auto it : myMap)
- 掌握
sort
函數(shù)的使用方法,包括自定義比較函數(shù)
快速輸入輸出技巧不能少
在比賽中,數(shù)據(jù)量大時(shí),用 cin
和 cout
會變慢。這時(shí)候可以用以下優(yōu)化手段:
ios::sync_with_stdio(false); cin.tie(nullptr);
這樣可以讓輸入更快。同時(shí)也可以改用 scanf
和 printf
,雖然不那么“C++”,但效率高。
還有一個(gè)小技巧是,如果題目要求多組測試數(shù)據(jù),可以在主函數(shù)外面聲明變量,避免重復(fù)構(gòu)造。
模板與宏簡化代碼書寫
比賽中時(shí)間寶貴,很多人會寫一些簡化的宏來節(jié)省時(shí)間。例如:
#define vi vector<int> #define pb push_back
或者更激進(jìn)一點(diǎn)的:
#define rep(i, a, b) for(int i = a; i < b; ++i)
不過要注意控制范圍,別搞得別人看不懂。模板也可以適當(dāng)用,比如寫一個(gè)通用的結(jié)構(gòu)體排序函數(shù)。
基本上就這些。剛開始可能會覺得東西很多,但多練幾道題,慢慢就熟了。C++ 在競賽里用得好,確實(shí)能提高效率。不復(fù)雜但容易忽略的地方,往往是調(diào)試時(shí)卡住的關(guān)鍵,比如邊界條件、初始化錯(cuò)誤或者迭代器失效這些細(xì)節(jié)。
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