交流程序的指针有问题

Question

I write the code that intends to perform an in-order traverse of a binary search tree and find the minimum absolute difference between values of any two nodes. I write this code and when I run this test case, instead of returning result 1, it throws result 2.

Here is the test case:

   2 
 /   \
1     4

Here is the code that I write:

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */

void inOrder(struct TreeNode* temp1, struct TreeNode* temp2, int* result) {
    if (temp1->left != NULL) {
        inOrder(temp1->left, temp2, result);
    }
    if (temp2 != NULL) {
        int dif = temp1 -> val - temp2 -> val;
        *result = *result > dif ? dif : *result;
    }
    printf("%p\n", temp2);
    temp2 = temp1;
    if (temp1->right != NULL) {
        inOrder(temp1->right, temp2, result);
    }
}

int getMinimumDifference(struct TreeNode* root) {
    int result  = 0x7fffffff;
    struct TreeNode* temp = NULL;
    inOrder(root, temp, &result);
    return result;
}

Here is the output of the printf:

(nil)
(nil)
0xfe72b0

As you can see, only the last node is not null. Which is abnormal since based on the logic of the code there should be two non-null printings.

So could you please help me solve this bug?

Answer 1

In your code temp2 is always NULL.
Try below snippet

void inOrder(struct TreeNode* temp1, struct TreeNode* temp2, int* result) {
    if (temp1->left != NULL) {
        inOrder(temp1->left, temp1, result);
    }
    if (temp2 != NULL) {
        int dif = temp1 -> val - temp2 -> val;
        if(dif < 0) dif *= -1; //absolute diff
        *result = *result > dif ? dif : *result;
    }
    printf("%p\n", temp2);
    //temp2 = temp1;
    if (temp1->right != NULL) {
        inOrder(temp1->right, temp1, result);
    }
}