Thread: Beginner's question

  1. #1
    Registered User
    Join Date
    May 2007

    Question Beginner's question

    Here's a sample code I came up for the following question :

    Given a tree and a sum, return true if there is a path from the root
    down to a leaf, such that adding up all the values along the path
    equals the given sum.

    Strategy: subtract the node value from the sum when recurring down,
    and check to see if the sum is 0 when you run out of tree.

    int subsums (TREE T, int sum){
    if (T==NULL){
    return (sum); 
    int subsum = sum - T->element; 
    return (subsums(T->left, subsum) && subsums(T->right, subsum));
    }// else

    if sum!=0 why is the result always printed as 1?
    int => it should print any value right? or does is convert to boolean ?

  2. #2
    Registered User
    Join Date
    May 2007

    Question Can any one please explain this

    For the same question above, the solution given was:

    int hasPathSum(struct tree_node* node, int sum) { 
      // return true if we run out of tree and sum==0 
      if (node == NULL) { 
        return(sum == 0); 
      else { 
      // otherwise check both subtrees 
        int subSum = sum - node->element; 
        return(hasPathSum(node->left, subSum) || 
               hasPathSum(node->right, subSum)); 
    I don't understand how if (node ==NULL) return (sum ==0) checks the logic (if sum == 0). Any help is greatly appreciated.

  3. #3
    Fear the Reaper...
    Join Date
    Aug 2005
    Toronto, Ontario, Canada
    The best thing to do in this case I think would be to take a sheet a paper, draw a tree on it, and run the algorithm by hand. You'll see what the NULL part if for.

    Basically, it checks that, once you reached a leaf, the accumulated sum is equal to the sum you began with.
    Teacher: "You connect with Internet Explorer, but what is your browser? You know, Yahoo, Webcrawler...?" It's great to see the educational system moving in the right direction

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