Kth bst

Signed-off-by: begeekmyfriend <begeekmyfriend@gmail.com>

Author: begeekmyfriend

230_kth_smallest_element_in_a_bst/Makefile

@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test kth_bst.c

230_kth_smallest_element_in_a_bst/kth_bst.c

@@ -0,0 +1,83 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+struct TreeNode {
+    int val;
+    struct TreeNode *left;
+    struct TreeNode *right;
+};
+
+static bool traverse(struct TreeNode *node, int *k, int *val)
+{
+    if (node == NULL) {
+        return false;
+    }
+    if (traverse(node->left, k, val)) {
+        return true;
+    }
+    if (--*k == 0) {
+        *val = node->val;
+        return true;
+    }
+    if (traverse(node->right, k, val)) {
+        return true;
+    }
+    return false;
+}
+
+static int kthSmallest(struct TreeNode* root, int k)
+{
+    int value = 0;
+    traverse(root, &k, &value);
+    return value;
+}
+
+int main(void)
+{
+#if 1
+    struct TreeNode root, n10, n11, n20, n21, n22, n23;
+    root.val = 1;
+    n10.val = 2;
+    n11.val = 2;
+    n20.val = 3;
+    n21.val = 4;
+    n22.val = 4;
+    n23.val = 3;
+    root.left = &n10;
+    root.right = &n11;
+    n10.left = &n20;
+    n10.right = &n21;
+    n11.left = &n22;
+    n11.right = &n23;
+    n20.left = NULL;
+    n20.right = NULL;
+    n21.left = NULL;
+    n21.right = NULL;
+    n22.left = NULL;
+    n22.right = NULL;
+    n23.left = NULL;
+    n23.right = NULL;
+#else
+    struct TreeNode root, n10, n11, n21, n22;
+    root.val = 1;
+    n10.val = 2;
+    n11.val = 2;
+    n21.val = 3;
+    n22.val = 4;
+    root.left = &n10;
+    root.right = &n11;
+    n10.left = NULL;
+    n10.right = &n21;
+    n11.left = &n22;
+    n11.right = NULL;
+    n21.left = NULL;
+    n21.right = NULL;
+    n22.left = NULL;
+    n22.right = NULL;
+#endif
+
+    int k = 1;
+    printf("%d\n", kthSmallest(&root, k));
+    return 0;
+}