iostream // 输入输出流
iomanip  // 操作符
cmath    // 数学函数
ctime    // clock, time, difftime, clock_t, time_t, CLOCKS_PER_SEC
cstdlib  // rand, srand, RAND_MAX, abs, system, exit 

cstring  // C语言字符串
cctype   // C语言字符
cstdio   // C语言文件操作: fopen, fclose, fread, fwrite, printf, scanf, sprintf

vector   // 向量类
string   // 字符串类
fstream  // 文件流

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