Example
Below shows an initialization of a sentinel node in a binary tree implemented in C programming language:
struct jsw_node { int data; int level; struct jsw_node *link; // link to next_left node; link to next_right node }; struct jsw_node *nil; // pointer to the sentinel node int jsw_init ( void ) { nil = (jsw_node*) malloc ( sizeof *nil ); // allocating memory for the sentinel node if ( nil == NULL ) // check for malloc failure return 0; // malloc failed to allocate memory nil->level = 0; nil->link = nil->link = nil; // link both right and left nodes to self (empty tree) return 1; // successful initialization }As nodes that would normally link to NULL now link to "nil" (including nil itself), it removes the need for an expensive branch operation to check for NULL. NULL itself is known as a sentinel value, a different approach to the same problem.
Read more about this topic: Sentinel Node
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