Library function -- (continuous update)

isdigit()： Judge whether the input characters are composed of numbers

	char ch;
	isdigit(ch)

Random function

srand((unsinged)(time(0)));  //  Random seeds 
int x = rand() % 100 // 0 ~ 100 Number of numbers 

Dichotomous function

//  Return is greater than the val The address of the value of 
upper_bound(a.begin(), a.end(), val);
upper_bound(a, a + n, val, val);

//  Return greater than or equal to val The address of the value of 
upper_lower(a.begin(), a.end(), val);
upper_lower(a, a + n, val);

Integer to string

int num;
string s = to_string(nmu);

Copy function （ Copy an array to another array ）

// vector<> Exchange of containers 
vector<int> a, b;
a.assign(b.begin(), b.end()); //  hold b Copy to a

// a[] The exchange of arrays 
int a[N], b[N];
memcpy(a, b, sizeof b); //  hold b Copy to a

sqrt() and log() The return value of the function is floating point

All permutation functions

// n by a The length of the array 
next_permutataion(a, a + n) //  Next in ascending order , namely  1 2 3 -> 1 3 2 -> 2 1 3 ... , 3 2 1 , And the next if there is a return 1, Otherwise return to 0
prev_permutation(a, a + n) // Next in descending order , namely  3 2 1 -> 3 1 2 ... 1 2 3, And the next if there is a return 1, Otherwise return to 0

Subsequences and substrings

Substring ： Successive
Subsequence ： It can be discontinuous

Definition of small root heap and large root heap

priority_queue<int> q; // Big root pile 
priority_queue<int, vector<int>, greater<int>> q; // Heap 

sort From big to small （2 Methods ）

int a[N];
sort(a, a + n, greater<int>()) // The in angle brackets are defined according to the array type 

bool cmp(int x, y)
{
    
	return x >= y;
}

int main()
{
    
	int a[N];
	sort(a, a + n, cmp);
}

All permutation functions （c++）

int a[N];
do
{
    
	...
}next_permutation(a, a + n); // Achieve ascending order 

do
{
    
	...
}prev_permutation(a, a + n) // Achieve descending order 

Dichotomous function

1. lower_bound()： Return greater than or equal to x Array subscript Address
2. upper_bound()： Return is greater than the x Array subscript Address
   If this number does not exist in the array , Then the array length will be returned .

int t = lower_bound(a, a + n, x) - a; // Because the return is the address , So we need to -a, That is, subtract the array name 
int t = upper_bound(a, a + n, x);