Time complexity and space complexity

Time complexity

First calculate the number of code executions T(n), Then the time complexity is estimated O(n).（ The total number of lines of code executed × Time required for each code sentence , Here, the time required for each code sentence is considered the same ）

Common time complexity ：

• O(1)、O(logn)、O(n)、O(nlogn)、O(n^2)

How to calculate ：

1）for、while loop

for(var i=0; i<n; i++){
    
    for(var j=0; j<n; ){
    
        j=j*2;
    }
}

Time complexity ：O(nlogn)

2） recursive

The number of recursions × The number of operations in each recursion

Spatial complexity

Amount of memory space occupied , Space complexity is used to express .

Common spatial complexity ：

• O(1)、O(n)、O(n^2)

How to calculate ：

• Variable ： How many variables are there , Then how many memory spaces have been opened up , Generally for arrays 、 Stack or something , How many values are stored takes up how much memory space
• recursive