Solve 230 with C++(DFS).

Author: illuz

solutions/230.Kth_Smallest_Element_in_a_BST/AC_dfs_n.cpp

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+/*
+*  Author:      illuz <iilluzen[at]gmail.com>
+*  File:        AC_dfs_n.cpp
+*  Create Date: 2015-08-14 10:21:47
+*  Descripton:   
+*/
+
+#include <bits/stdc++.h>
+
+using namespace std;
+const int N = 0;
+
+// Definition for a binary tree node.
+struct TreeNode {
+    int val;
+    TreeNode *left;
+    TreeNode *right;
+    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+};
+
+class Solution {
+public:
+    int kthSmallest(TreeNode* root, int k) {
+        ans = 0;
+        flag = false;
+        dfs(root, k);
+        return ans;
+    }
+
+private:
+    int ans;
+    bool flag;
+    // this return size of a tree
+    int dfs(TreeNode* root, int k) {
+        // if found the ans
+        if (flag) return 0;
+        if (root == NULL) return 0;
+        int leftsize = dfs(root->left, k);
+        if (k - leftsize == 1) {
+            ans = root->val;
+            flag = true;
+        }
+        int rightsize = dfs(root->right, k - leftsize - 1);
+        return leftsize + rightsize + 1;
+    }
+};
+
+int main() {
+
+    return 0;
+}
+