General

• 
• 万能: #include<bits/stdc++.h>

Vector

• find:
  • vector没有"count"!

auto p = find(v.begin(), v.end(), "ab");

• erase:

v.erase(v.begin() + 1);  // vector要用pointer删除

• insert:

v.insert(v.begin(), "abc");  // for vector<string>

• swap:

vector<int> f = {1, 2, 3};
swap(f[0], f[2])   // {3, 2, 1}

• 2D array:

vector<vector<int>> four_ways = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
vector<vector<int>> dp(5, vector<int>(4, 0));

Unordered_set

• count:

int n = s.count(4);

• erase:

int n = s.erase("abc");  // can be void as well; return 1 if exist, 0 if not

Unordered_map

Binary Search

• upper_bound:

• lower_bound: