"Count Complete Tree Nodes"

Author: lennylxx

README.md

@@ -23,7 +23,7 @@ Compile **C++** files using command:
 | 225 | [Implement Stack using Queues]                               | [C](src/225.c)     |
 | 224 | [Basic Calculator]                                           | [C](src/224.c)     |
 | 223 | [Rectangle Area]                                             | [C](src/223.c)     |
-| 222 | [Count Complete Tree Nodes]                                  |                    |
+| 222 | [Count Complete Tree Nodes]                                  | [C](src/222.c)     |
 | 221 | [Maximal Square]                                             |                    |
 | 220 | [Contains Duplicate III]                                     |                    |
 | 219 | [Contains Duplicate II]                                      |                    |

src/222.c

@@ -0,0 +1,68 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+struct TreeNode {
+    int val;
+    struct TreeNode *left;
+    struct TreeNode *right;
+};
+
+int countNodes(struct TreeNode* root) {
+    if (root == NULL) return 0;
+
+    struct TreeNode *l = root->left;
+    struct TreeNode *r = root->right;
+
+    int most_left_height = 1;
+    int most_right_height = 1;
+
+    while (l != NULL) {
+        l = l->left;
+        most_left_height++;
+    }
+
+    while (r != NULL) {
+        r = r->right;
+        most_right_height++;
+    }
+
+    if (most_left_height == most_right_height) { /* it's a full binary tree */
+        return (1 << most_left_height) - 1;
+    }
+    else {
+        return countNodes(root->left) + countNodes(root->right) + 1;
+    }
+}
+
+int main() {
+
+    struct TreeNode *r = (struct TreeNode *)calloc(9, sizeof(struct TreeNode));
+    struct TreeNode *p = r;
+
+    int i;
+    for (i = 1; i <= 9; i++) {
+        p->val = i;
+        p++;
+    }
+
+    p = r;
+    p->left = r + 1;
+    p->right = r + 2;
+
+    p = r + 1;
+    p->left = r + 3;
+    p->right = r + 4;
+
+    p = r + 2;
+    p->left = r + 5;
+    p->right = r + 6;
+
+    p = r + 3;
+    p->left = r + 7;
+    p->right = r + 8;
+
+    /* should be 9 */
+    printf("%d\n", countNodes(r));
+
+    return 0;
+}