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  1. #include<stdio.h>
  2. #include<malloc.h>
  3.  
  4. struct binaryTreeNode{
  5. 	int data;
  6. 	struct binaryTreeNode * left;
  7. 	struct binaryTreeNode * right;
  8. };
  9.  
  10. struct node
  11. {
  12. 	struct binaryTreeNode * data;
  13. 	struct node * next;
  14. };
  15.  
  16. struct queue
  17. {
  18. 	struct node * front;
  19. 	struct node * rear;
  20. };
  21.  
  22. struct queue * enQueue(struct queue * q, struct binaryTreeNode * num)
  23. {
  24. 	struct node * temp = (struct node*)malloc(sizeof(struct node));
  25. 	temp -> data = num;
  26. 	temp -> next = NULL;
  27. 	if(q == NULL)
  28. 	{
  29. 		q = (struct queue*)malloc(sizeof(struct queue));		
  30. 		q -> front = temp;
  31. 	}
  32. 	else
  33. 		q -> rear -> next = temp;
  34. 	q -> rear = temp;
  35. 	//Code obtained from http://w...content-available-to-author-only...s.com
  36. 	//Feel free to copy but please acknowledge the site wherever possible
  37. 	return q;
  38. }
  39.  
  40. struct queue * deQueue(struct queue * q)
  41. {
  42. 	struct node * temp = q->front;
  43. 	q -> front = q->front->next;
  44. 	free(temp);
  45. 	if(q->front == NULL)
  46. 		return NULL;
  47. 	else
  48. 		return q;
  49. }
  50.  
  51. int isQueueEmpty(struct queue * q)
  52. {
  53. 	if(q)
  54. 		return 0;
  55. 	else
  56. 		return 1;
  57. }
  58.  
  59. void leftViewOfBinaryTree(struct binaryTreeNode * root)
  60. {
  61. 	// Level order traversal
  62. 	struct binaryTreeNode * temp = NULL;
  63. 	struct queue * Q = NULL;
  64.  
  65. 	// Maintain a level count
  66. 	int level = 0;
  67.  
  68. 	if(root == NULL)
  69. 		return;
  70.  
  71. 	Q = enQueue(Q, root);
  72.  
  73. 	//print the root
  74. 	printf("%d ",root->data);
  75.  
  76. 	int needToPrint = 0;
  77.  
  78. 	// Now the first level will end over here,
  79. 	// So append a NULL node
  80. 	Q = enQueue(Q, NULL);
  81.  
  82. 	while(!isQueueEmpty(Q))
  83. 	{
  84. 		temp = Q -> front -> data;
  85. 		Q = deQueue(Q);
  86.  
  87. 		if(needToPrint)
  88. 		{
  89. 			printf("%d ", temp->data);
  90. 			needToPrint = 0;
  91. 		}
  92.  
  93. 		// If we encounter a NULL, that means an end of a level
  94. 		// And we need to increment the level count
  95. 		if(temp == NULL)
  96. 		{
  97. 			// Put the marker for next level also
  98. 			if(!isQueueEmpty(Q))
  99. 				Q = enQueue(Q, NULL);
  100.  
  101. 			level++;
  102. 			needToPrint = 1;
  103. 		}
  104. 		else
  105. 		{
  106. 			// We continue with the level order traversal
  107. 			if(temp -> left)
  108. 				Q = enQueue(Q, temp -> left);
  109. 			if(temp -> right)
  110. 				Q = enQueue(Q, temp -> right);
  111. 		}
  112. 	}
  113. 	// Delete the queue
  114. 	free(Q);
  115. }
  116.  
  117. // Test the above functions
  118. int main(void)
  119. {
  120. 	// Initialize the tree
  121. 	struct binaryTreeNode * root = (struct binaryTreeNode *)malloc(sizeof(struct binaryTreeNode));
  122. 	root-> data = 1;
  123. 	struct binaryTreeNode * l = (struct binaryTreeNode *)malloc(sizeof(struct binaryTreeNode));
  124. 	l -> data = 2;
  125. 	struct binaryTreeNode * ll = (struct binaryTreeNode *)malloc(sizeof(struct binaryTreeNode));
  126. 	ll -> data = 4;
  127. 	ll -> left = ll -> right = NULL;
  128. 	struct binaryTreeNode * lr = (struct binaryTreeNode *)malloc(sizeof(struct binaryTreeNode));
  129. 	lr -> data = 5;
  130. 	lr -> left = lr -> right = NULL;
  131. 	l -> left = ll;
  132. 	l -> right = lr;
  133. 	struct binaryTreeNode * r = (struct binaryTreeNode *)malloc(sizeof(struct binaryTreeNode));
  134. 	r -> data = 3;
  135. 	struct binaryTreeNode * rl = (struct binaryTreeNode *)malloc(sizeof(struct binaryTreeNode));
  136. 	rl -> data = 6;
  137. 	rl -> left = rl -> right = NULL;
  138. 	struct binaryTreeNode * rr = (struct binaryTreeNode *)malloc(sizeof(struct binaryTreeNode));
  139. 	rr -> data = 7;
  140. 	rr -> left = rr -> right = NULL;
  141. 	r -> left = rl;
  142. 	r -> right = rr;
  143. 	root -> left = l;
  144. 	root -> right = r;
  145.  
  146. 	printf("Left view of tree = ");
  147. 	leftViewOfBinaryTree(root);
  148.  
  149. 	return 0;
  150. }
Success #stdin #stdout 0s 2380KB
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stdout
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Left view of tree = 1 2 4
https://ideone.com/PaJPER
language:
C (gcc 8.3)
created:
10 years ago
visibility:
public

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