Refine

Signed-off-by: begeekmyfriend <[email protected]>

Author: begeekmyfriend

098_validate_binary_search_tree/valid_bst.c

@@ -3,24 +3,34 @@
 #include <stdbool.h>
 #include <limits.h>
 
+
 struct TreeNode {
     int val;
     struct TreeNode *left;
     struct TreeNode *right;
 };
 
-static bool dfs(struct TreeNode* node, int min, int max)
-{
-    if (node == NULL) return true;
-    if (node->val < min || node->val > max) return false;
-    if (node->left != NULL && node->val == INT_MIN) return false;
-    if (node->right != NULL && node->val == INT_MAX) return false;
-    return dfs(node->left, min, node->val - 1) && dfs(node->right, node->val + 1, max);
-}
-
-static bool isValidBST(struct TreeNode* root)
+bool isValidBST(struct TreeNode* root)
 {
-    return dfs(root, INT_MIN, INT_MAX);
+    int top = 0;
+    int prev = INT_MIN;
+    bool first = true;
+    struct TreeNode *stack[1000];
+    while (top > 0 || root != NULL) {
+        if (root != NULL) {
+            stack[top++] = root;
+            root = root->left;
+        } else {
+            root = stack[--top];
+            if (!first && prev >= root->val) {
+                return false;
+            }
+            first = false;
+            prev = root->val;
+            root = root->right;
+        }
+    }
+    return true;
 }
 
 int main(int argc, char **argv)

099_recover_binary_search_tree/recover_bst.c

@@ -2,48 +2,48 @@
 #include <stdlib.h>
 #include <stdbool.h>
 
+
 struct TreeNode {
     int val;
     struct TreeNode *left;
     struct TreeNode *right;
 };
 
-static void traverse(struct TreeNode *node, struct TreeNode **prev,
-                     struct TreeNode **p1, struct TreeNode **p2, int *wrong)
+static void dfs(struct TreeNode *node, struct TreeNode **prev,
+                struct TreeNode **p1, struct TreeNode **p2, int *wrong)
 {
-    if (node->left != NULL) {
-        traverse(node->left, prev, p1, p2, wrong);
+    if (node == NULL || *wrong == 2) {
+        return;
     }
 
+    dfs(node->left, prev, p1, p2, wrong);
+
+    /* We must use pointer to pointer for previous object in recursion */
     if (*prev != NULL && node->val < (*prev)->val) {
         (*wrong)++;
         if (*wrong == 1) {
             *p1 = *prev;
+            /* p2 should be recorded here in some cases */
             *p2 = node;
         } else if (*wrong == 2) {
             *p2 = node;
-            return;
         }
     }
     *prev = node;
 
-    if (node->right != NULL) {
-        traverse(node->right, prev, p1, p2, wrong);
-    }
+    dfs(node->right, prev, p1, p2, wrong);
 }
 
 static void recoverTree(struct TreeNode* root)
 {
-    if (root != NULL) {
-        struct TreeNode *prev = NULL;
-        struct TreeNode *p1 = NULL;
-        struct TreeNode *p2 = NULL;
-        int wrong = 0;
-        traverse(root, &prev, &p1, &p2, &wrong);
-        int tmp = p1->val;
-        p1->val = p2->val;
-        p2->val = tmp;
-    }
+    int wrong = 0;
+    struct TreeNode *prev = NULL;
+    struct TreeNode *p1 = NULL;
+    struct TreeNode *p2 = NULL;
+    dfs(root, &prev, &p1, &p2, &wrong);
+    int tmp = p1->val;
+    p1->val = p2->val;
+    p2->val = tmp;
 }
 
 int main(int argc, char **argv)

100_same_tree/same_tree.c

@@ -10,21 +10,16 @@ struct TreeNode {
 
 static bool isSameTree(struct TreeNode* p, struct TreeNode* q)
 {
-    if (p != NULL && q != NULL) {
-        if (p->val != q->val) {
-            return false;
-        }
-        if (!isSameTree(p->left, q->left)) {
-            return false;
-        }
-        if (!isSameTree(p->right, q->right)) {
-            return false;
-        }
-    } else {
-        return p == q;
+    if (p == NULL && q == NULL) {
+        return true;
     }
-
-    return true;
+    if (p == NULL || q == NULL) {
+        return false;
+    }
+    if (p->val != q->val) {
+        return false;
+    }
+    return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
 }
 
 int main(void)

198_house_robber/robber.c

@@ -20,6 +20,7 @@ static int rob(int* nums, int numsSize)
     for (i = 1; i < numsSize; i++) {
         int tmp_taken = taken;
         int tmp_untaken = untaken;
+        /* Taken or untaken nums[i] */
         taken = untaken + nums[i];
         untaken = max(tmp_taken, tmp_untaken);
     }

213_house_robber_ii/robber.c

@@ -16,6 +16,7 @@ static int _rob(int* nums, int numsSize)
     for (i = 1; i < numsSize; i++) {
         int tmp_taken = taken;
         int tmp_untaken = untaken;
+        /* Taken or untaken nums[i] */
         taken = tmp_untaken + nums[i];
         untaken = max(tmp_taken, tmp_untaken);
     }