Iterative Tree Traversals

The below functions assume that a stack of type pointer to Node is already created which supports push and pop operations.

Preorder Traversal :

void preorderTraversal(struct Node *ptr) {
​
// A stack to keep track of visited nodes
struct Stack s;
// Iterate until pointer is not NULL or stack is not empty
while (ptr != NULL || !isEmpty(s)) {
if (ptr) {
printf("%d\t", ptr -> data);
// Push current node address to stack
push(&s, p);
ptr = ptr -> left;
} else {
ptr = pop(&s);
ptr = ptr -> right;
}
}
​
}

Inorder Traversal :

void inorderTraversal(struct Node *ptr) {
​
// A stack to keep track of visited nodes
struct Stack s;
// Iterate until pointer is not NULL or stack is not empty
while (ptr != NULL || !isEmpty(s)) {
if (ptr) {
// Push current node address to stack
push(&s, p);
ptr = ptr -> left;
} else {
ptr = pop(&s);
printf("%d\t", ptr -> data);
ptr = ptr -> right;
}
}
​
}

Postorder Traversal :

void postorderTraversal(struct Node *ptr) {
​
// A stack to keep track of visited nodes
struct Stack s;
// Iterate until pointer is not NULL or stack is not empty
while (ptr != NULL || !isEmpty(s)) {
if (ptr) {
// Push current node address to stack
push(&s, p);
ptr = ptr -> left;
} else {
ptr = pop(&s);
ptr = ptr -> right;
printf("%d\t", ptr -> data);
}
}
​
}
​
Contributed by Nitin Ranganath