演算法 Algorithm

演算法的運作時間(步數)

O = 算法的時間上限
Ω = 算法的時間下限
θ = 算法上限 == 算法下限
ex. O(n^2), O(n), O(log n), O(1)

搜尋 Search

線性搜尋法 Linear Search => O(n)、Ω(1)

for each door from left to right
    if nubere is behind door
        return true
    else
        return false

二分搜尋法 Binary Search => O(log n)、Ω(1)

if no doors
    return false
if number behind middle door
    return true
else if number < middle door
    search left half
else if number > middle door
    search right half

排序 Sort

選擇排序 Selection Sort => ~θ(n^2)
=> comparing sort

for i from 0 to n-1
    find smallest number between numbers[i] and numbers[n-1]
    swap smallest number between numbers[i]

泡沫排序 Bubble Sort => ~O(n^2)、Ω(n-1)
=> comparing sort

repeat n-1 times
    for i from 0 to n-2
        if numbers[i] and numbers[i+1] out of order
            swap them

合併排序 Merge Sort => θ(log n)
=> recursion sort

If only one number
    quit
Else
    Sort left half of numbers
    Sort right half of numbers
    merge sorted halves

Data Structure 自定型態

typedef struct
{
    string name;
    string number;
}
person;

int main(void)
{
person people;
people[0].name = "Penny";
people[0].number = "1995";

people[1].name = "Leo";
people[1].number = "1996";

for (int i = 0; i < 2; i++)
{
    if(strcmp(peolple[i].name) == 0)
    {
        printf("%s\n", people[i].number);
        return 0;
    }
}
printf("not found.\n")
return 1;
}

偽代碼 (虛擬代碼) pseudocode
介於自然語言(English)程式語言(code)之間的描述法。

遞迴 Recursion
function that call itself