Represent null with INT_MAX in C, C++.

codes/c/CMakeLists.txt

@@ -10,5 +10,7 @@ add_subdirectory(chapter_computational_complexity)
 add_subdirectory(chapter_array_and_linkedlist)
 add_subdirectory(chapter_stack_and_queue)
 add_subdirectory(chapter_binary_search)
+add_subdirectory(chapter_tree)
 add_subdirectory(chapter_heap)
 add_subdirectory(chapter_searching)
+add_subdirectory(chapter_sorting)

codes/c/chapter_heap/my_heap.c

@@ -90,7 +90,7 @@ int pop(maxHeap *h) {
     // 判空处理
     if (isEmpty(h)) {
         printf("heap is empty!");
-        return NIL;
+        return INT_MAX;
     }
     // 交换根节点与最右叶节点（即交换首元素与尾元素）
     swap(h, 0, size(h) - 1);

codes/c/chapter_searching/leetcode_two_sum.c

@@ -11,10 +11,10 @@ int *twoSumBruteForce(int *nums, int numsSize, int target, int *returnSize) {
     for (int i = 0; i < numsSize; ++i) {
         for (int j = i + 1; j < numsSize; ++j) {
             if (nums[i] + nums[j] == target) {
-                int *ret = malloc(sizeof(int) * 2);
-                ret[0] = i, ret[1] = j;
+                int *res = malloc(sizeof(int) * 2);
+                res[0] = i, res[1] = j;
                 *returnSize = 2;
-                return ret;
+                return res;
             }
         }
     }
@@ -32,12 +32,14 @@ struct hashTable {
 
 typedef struct hashTable hashTable;
 
+/* 哈希表查询 */
 hashTable *find(hashTable *h, int key) {
     hashTable *tmp;
     HASH_FIND_INT(h, &key, tmp);
     return tmp;
 }
 
+/* 哈希表元素插入 */
 void insert(hashTable *h, int key, int val) {
     hashTable *t = find(h, key);
     if (t == NULL) {
@@ -55,10 +57,10 @@ int *twoSumHashTable(int *nums, int numsSize, int target, int *returnSize) {
     for (int i = 0; i < numsSize; i++) {
         hashTable *t = find(hashtable, target - nums[i]);
         if (t != NULL) {
-            int *ret = malloc(sizeof(int) * 2);
-            ret[0] = t->val, ret[1] = i;
+            int *res = malloc(sizeof(int) * 2);
+            res[0] = t->val, res[1] = i;
             *returnSize = 2;
-            return ret;
+            return res;
         }
         insert(hashtable, nums[i], i);
     }

codes/c/chapter_stack_and_queue/array_stack.c

@@ -48,7 +48,7 @@ void push(arrayStack *s, int num) {
 int peek(arrayStack *s) {
     if (s->size == 0) {
         printf("stack is empty.\n");
-        return NIL;
+        return INT_MAX;
     }
     return s->data[s->size - 1];
 }
@@ -57,7 +57,7 @@ int peek(arrayStack *s) {
 int pop(arrayStack *s) {
     if (s->size == 0) {
         printf("stack is empty.\n");
-        return NIL;
+        return INT_MAX;
     }
     int val = peek(s);
     s->size--;

codes/c/chapter_stack_and_queue/linkedlist_stack.c

@@ -65,7 +65,7 @@ void push(linkedListStack *s, int num) {
 int pop(linkedListStack *s) {
     if (s->size == 0) {
         printf("stack is empty.\n");
-        return NIL;
+        return INT_MAX;
     }
     assert(s);
     int val = peek(s);

codes/c/chapter_tree/avl_tree.c

@@ -30,7 +30,7 @@ int height(TreeNode *node) {
 }
 
 /* 更新节点高度 */
-int updateHeight(TreeNode *node) {
+void updateHeight(TreeNode *node) {
     int lh = height(node->left);
     int rh = height(node->right);
     // 节点高度等于最高子树高度 + 1

codes/c/chapter_tree/binary_tree_bfs.c

@@ -49,7 +49,7 @@ int *levelOrder(TreeNode *root, int *size) {
 int main() {
     /* 初始化二叉树 */
     // 这里借助了一个从数组直接生成二叉树的函数
-    int nums[] = {1, 2, 3, NIL, 5, 6, NIL};
+    int nums[] = {1, 2, 3, 4, 5, 6, 7};
     int size = sizeof(nums) / sizeof(int);
     TreeNode *root = arrToTree(nums, size);
     printf("初始化二叉树\n");

codes/c/include/include_test.c

@@ -17,7 +17,7 @@ void testListNode() {
 }
 
 void testTreeNode() {
-    int nums[] = {1, 2, 3, NIL, 5, 6, NIL};
+    int nums[] = {1, 2, 3, INT_MAX, 5, 6, INT_MAX};
     int size = sizeof(nums) / sizeof(int);
     TreeNode *root = arrToTree(nums, size);
 

codes/c/include/print_util.h

@@ -23,13 +23,13 @@ static void printArray(int arr[], int size) {
     printf("[");
     if (arr != NULL && size != 0) {
         for (int i = 0; i < size - 1; i++) {
-            if (arr[i] != NIL) {
+            if (arr[i] != INT_MAX) {
                 printf("%d, ", arr[i]);
             } else {
                 printf("NULL, ");
             }
         }
-        if (arr[size - 1] != NIL) {
+        if (arr[size - 1] != INT_MAX) {
             printf("%d]\n", arr[size - 1]);
         } else {
             printf("NULL]\n");

codes/c/include/tree_node.h

@@ -11,7 +11,8 @@
 extern "C" {
 #endif
 
-#define NIL ('#')
+#include <limits.h>
+
 #define MAX_NODE_SIZE 5000
 
 struct TreeNode {
@@ -59,14 +60,15 @@ TreeNode *arrToTree(const int *arr, size_t size) {
         node = queue[front++];
         index++;
         if (index < size) {
-            if (arr[index] != NIL) {
+            // represent null with INT_MAX 
+            if (arr[index] != INT_MAX) {
                 node->left = newTreeNode(arr[index]);
                 queue[rear++] = node->left;
             }
         }
         index++;
         if (index < size) {
-            if (arr[index] != NIL) {
+            if (arr[index] != INT_MAX) {
                 node->right = newTreeNode(arr[index]);
                 queue[rear++] = node->right;
             }
@@ -102,7 +104,7 @@ int *treeToArr(TreeNode *root) {
             queue[rear++] = node->left;
             queue[rear++] = node->right;
         } else {
-            arr[index] = NIL;
+            arr[index] = INT_MAX;
         }
         index++;
     }

codes/cpp/include/TreeNode.hpp

@@ -6,6 +6,8 @@
 
 #pragma once
 
+#include <limits.h>
+
 /* Definition for a binary tree node */
 struct TreeNode {
     int val{};
@@ -26,20 +28,21 @@ TreeNode *vecToTree(vector<int> list) {
     auto *root = new TreeNode(list[0]);
     queue<TreeNode *> que;
     que.emplace(root);
-    size_t n = list.size(), index = 0;
+    size_t n = list.size(), i = 0;
     while (!que.empty()) {
         auto node = que.front();
         que.pop();
-        if (++index >= n)
+        if (++i >= n)
             break;
-        if (index < n) {
-            node->left = new TreeNode(list[index]);
+        // INT_MAX represent null
+        if (list[i] != INT_MAX) {
+            node->left = new TreeNode(list[i]);
             que.emplace(node->left);
         }
-        if (++index >= n)
+        if (++i >= n)
             break;
-        if (index < n) {
-            node->right = new TreeNode(list[index]);
+        if (list[i] != INT_MAX) {
+            node->right = new TreeNode(list[i]);
             que.emplace(node->right);
         }
     }