Created
August 13, 2018 14:11
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A cheat sheet or reference card of basic algorithm in C
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#include <stdlib.h> | |
#include <string.h> | |
static void swap(int *a, int *b) { | |
if (a != b) { | |
int c = *a; | |
*a = *b; | |
*b = c; | |
} | |
} | |
void bubblesort(int *a, int l) { | |
int i, j; | |
for (i = l - 2; i >= 0; i--) | |
for (j = i; j < l - 1 && a[j] > a[j + 1]; j++) | |
swap(a + j, a + j + 1); | |
} | |
void selectionsort(int *a, int l) { | |
int i, j, k; | |
for (i = 0; i < l; i++) { | |
for (j = (k = i) + 1; j < l; j++) | |
if (a[j] < a[k]) | |
k = j; | |
swap(a + i, a + k); | |
} | |
} | |
static void hsort_helper(int *a, int i, int l) { | |
int j; | |
for (j = 2 * i + 1; j < l; i = j, j = 2 * j + 1) | |
if (a[i] < a[j]) | |
if (j + 1 < l && a[j] < a[j + 1]) | |
swap(a + i, a + ++j); | |
else | |
swap(a + i, a + j); | |
else if (j + 1 < l && a[i] < a[j + 1]) | |
swap(a + i, a + ++j); | |
else | |
break; | |
} | |
void heapsort(int *a, int l) { | |
int i; | |
for (i = (l - 2) / 2; i >= 0; i--) | |
hsort_helper(a, i, l); | |
while (l-- > 0) { | |
swap(a, a + l); | |
hsort_helper(a, 0, l); | |
} | |
} | |
static void msort_helper(int *a, int *b, int l) { | |
int i, j, k, m; | |
switch (l) { | |
case 1: | |
a[0] = b[0]; | |
case 0: | |
return; | |
} | |
m = l / 2; | |
msort_helper(b, a, m); | |
msort_helper(b + m, a + m, l - m); | |
for (i = 0, j = 0, k = m; i < l; i++) | |
a[i] = b[j < m && !(k < l && b[j] > b[k]) ? j++ : k++]; | |
} | |
void mergesort(int *a, int l) { | |
int *b; | |
if (l < 0) | |
return; | |
b = malloc(l * sizeof(int)); | |
memcpy(b, a, l * sizeof(int)); | |
msort_helper(a, b, l); | |
free(b); | |
} | |
static int pivot(int *a, int l) { | |
int i, j; | |
for (i = j = 1; i < l; i++) | |
if (a[i] <= a[0]) | |
swap(a + i, a + j++); | |
swap(a, a + j - 1); | |
return j; | |
} | |
void quicksort(int *a, int l) { | |
int m; | |
if (l <= 1) | |
return; | |
m = pivot(a, l); | |
quicksort(a, m - 1); | |
quicksort(a + m, l - m); | |
} | |
struct node { | |
int value; | |
struct node *left, *right; | |
}; | |
void btreesort(int *a, int l) { | |
int i; | |
struct node *root = NULL, **ptr; | |
for (i = 0; i < l; i++) { | |
for (ptr = &root; *ptr;) | |
ptr = a[i] < (*ptr)->value ? &(*ptr)->left : &(*ptr)->right; | |
*ptr = malloc(sizeof(struct node)); | |
**ptr = (struct node){.value = a[i]}; | |
} | |
for (i = 0; i < l; i++) { | |
struct node *node; | |
for (ptr = &root; (*ptr)->left; ptr = &(*ptr)->left); | |
a[i] = (*ptr)->value; | |
node = (*ptr)->right; | |
free(*ptr); | |
(*ptr) = node; | |
} | |
} |
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https://stackoverflow.com/questions/244252/a-good-reference-card-cheat-sheet-with-the-basic-sort-algorithms-in-c