90. 구조체 노드로 만든 이진 트리의 세 가지 순회

1#include <stdio.h>
2#include <stdlib.h>
3 
4struct Node {
5    char key;
6    struct Node *left;
7    struct Node *right;
8};
9 
10struct Node *make(char k, struct Node *l, struct Node *r) {
11    struct Node *n = (struct Node *)malloc(sizeof(struct Node));
12    n->key = k;
13    n->left = l;
14    n->right = r;
15    return n;
16}
17 
18void walk(struct Node *t, int mode) {
19    if (t == NULL) return;
20    if (mode == 0) printf("%c", t->key);
21    walk(t->left, mode);
22    if (mode == 1) printf("%c", t->key);
23    walk(t->right, mode);
24    if (mode == 2) printf("%c", t->key);
25}
26 
27void release(struct Node *t) {
28    if (t == NULL) return;
29    release(t->left);
30    release(t->right);
31    free(t);
32}
33 
34int main() {
35    struct Node *g = make('G', NULL, NULL);
36    struct Node *d = make('D', NULL, g);
37    struct Node *p = make('P', NULL, NULL);
38    struct Node *t = make('T', p, NULL);
39    struct Node *root = make('M', d, t);
40    for (int m = 0; m < 3; m++) {
41        walk(root, m);
42        printf("\n");
43    }
44    release(root);
45    return 0;
46}