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+// 590. N-ary Tree Postorder Traversal
+#include "leetcode.h"
+
+/*
+ * given the 'root' of an n-ary tree, return the postorder traversal of its
+ * nodes' values. nary-tree input serialisation is represented in their level
+ * order traversal. each group of children is separated by the null value.
+ */
+
+void *post_vis(struct Node *root, int *n, int *idx) {
+ int i = 0, cnt[1000] = {0};
+ struct Node *prev[1000];
+ prev[i++] = NULL;
+ while (root) {
+ if (root->numChildren == cnt[i]) {
+ n[(*idx)++] = root->val;
+ cnt[i--] = 0;
+ root = prev[i];
+ } else {
+ prev[i] = root;
+ root = root->children[cnt[i++]++];
+ }
+ }
+ return NULL;
+}
+
+int *postorder(struct Node *root, int *returnSize) {
+ int *n = (int *)calloc(10000, sizeof(int)), idx = 0;
+ post_vis(root, n, &idx);
+ *returnSize = idx;
+ return n;
+}
+
+int main() {
+ struct Node *root = node_create(1, 3);
+ root->children[0] = node_create(3, 2);
+ root->children[1] = node_create(2, 0);
+ root->children[2] = node_create(4, 0);
+ root->children[0]->children[0] = node_create(5, 0);
+ root->children[0]->children[1] = node_create(6, 0);
+ int rs, *p = postorder(root, &rs);
+ for (int i = 0; i < rs; i++)
+ printf("%d ", p[i]); // expect: 5 6 3 2 4 1
+ free(p);
+}