cours_3.md

title: "Introduction aux algorithmes"
date: "2022-10-05"
patat:
  eval:
    tai:
      command: fish
      fragment: false
      replace: true
    ccc:
      command: fish
      fragment: false
      replace: true
  images:
    backend: auto
int main() {
    int m = 15, n = 12;
    int mult_m = m, mult_n = n;
    while (mult_m != mult_n) {
        if (mult_m > mult_n) {
            mult_n += n;
        } else {
            mult_m += m;
        }
    }
    printf("Le ppcm de %d et %d est %d\n", n, m, mult_m);
}
PGCD(3, 4) = 1,
PGCD(4, 6) = 2,
PGCD(5, 15) = 5.
PGCD(36, 90):
90 % 36 != 0 // otherwise 36 would be PGCD
90 % 35 != 0 // otherwise 35 would be PGCD
90 % 34 != 0 // otherwise 34 would be PGCD
...
90 % 19 != 0 // otherwise 19 would be PGCD
90 % 18 == 0 // The end!
void main() {
   int n = 90, m = 78;
   int gcd = 1;
   for (int div = n; div >= 2; div--) { // div = m, sqrt(n)
      if (n % div == 0 && m % div == 0) {
         gcd = div;
         break;
      }
   }
   printf("Le pgcd de %d et %d est %d\n", n, m, gcd);
}
PGCD(35, 60):
35 = 60 * 0 + 35 // 60 -> 35, 35 -> 60
60 = 35 * 1 + 25 // 35 -> 60, 25 -> 35
35 = 25 * 1 + 10 // 25 -> 35, 20 -> 25
25 = 10 * 2 +  5 // 10 -> 25, 5  -> 10
10 =  5 * 2 +  0 // PGCD = 5!
entier pgcd(m, n) {
    tmp_n = n
    tmp_m = m
    tant que (tmp_m ne divise pas tmp_n) {
        tmp   = tmp_n
        tmp_n = tmp_m
        tmp_m = tmp modulo tmp_m
    }
    retourne tmp_m
}
#include <stdio.h>
void main() {
   int n = 90;
   int m = 78;
   printf("n = %d et m = %d\n", n, m);
   int tmp_n = n;
   int tmp_m = m;
   while (tmp_n%tmp_m > 0) {
      int tmp = tmp_n;
      tmp_n = tmp_m;
      tmp_m = tmp % tmp_m;
   }
   printf("Le pgcd de %d et %d est %d\n", n, m, tmp_m);
}
#define SIZE 10
int entiers[] = {2, 1, 4, 5, 7}; // taille 5, initialisé
int tab[3]; // taille 3, non initialisé
float many_floats[SIZE]; // taille 10, non initialisé
int premier = entier[0]; // premier = 2
int dernier = entier[4]; // dernier = 7
int indetermine_1 = tab[1];     // undefined behavior
int indetermine_2 = entiers[5]; // UB
int size;
scanf("%d", &size);
char string[size];
double tab[4];
#define SIZE 10
double tab[SIZE];
for (int i = 0; i < SIZE; ++i) {
    tab[i] = rand() / (double)RAND_MAX * 10.0 - 5.0;
    // tab[i] contient un double dans [-5;5]
}
index = 0
min   = tab[0]
for i in [1; SIZE] {
    if min > tab[i] {
        min = tab[i]
        index = i
    }
}
int index = 0;
float min = tab[0];
for (int i = 1; i < SIZE; ++i) {
    if min > tab[i] {
        min = tab[i];
        index = i;
    }
}
ind = 0
tant que (ind < SIZE-1)
    Trouver le minimum du tableau, tab_min[ind:SIZE].
    Échanger tab_min avec tab[ind]
    ind += 1
string = tableau + char + magie noire
char c = 'A';
char c = 65;
char *str  = "HELLO !";
char str[] = "HELLO !";
char name[5];
name[0] = 'P';  // = 70;
name[1] = 'a';  // = 97;
name[2] = 'u';  // = 117;
name[3] = 'l';  // = 108;
name[4] = '\0'; // = 0;
char name[] = {'P', 'a', 'u', 'l', '\0'};
char name[5] = "Paul";
char name[] = "Paul";
char name[100] = "Paul is not 100 characters long.";
// longueur de la chaîne (sans le \0)
size_t strlen(char *str);
// copie jusqu'à un \0
char *strcpy(char *dest, const char *src);
 // copie len char
char *strncpy(char *dest, const char *src, size_t len);
// compare len chars
int strncmp(char *str1, char *str2, size_t len);
// compare jusqu'à un \0
int strcmp(char *str1, char *str2);
int main() { // pseudo C
    tri(mot1);
    tri(mot2);
    if egalite(mot1, mot2) {
        // anagrammes
    } else {
        // pas anagrammes
    }
}
while (first_index < last_index {
    if (mot[first_index] != mot [last_index]) {
        return false;
    }
    first_index += 1;
    last_index -= 1;
}
return true;
mot_tmp = revert(mot);
return mot == mot_tmp;