Find the Duplicate Number

Author: ishpreet-singh

23.cpp

@@ -0,0 +1,32 @@
+/*
+
+Count Complete Tree Nodes
+-------------------------
+
+Given a complete binary tree, count the number of nodes.
+
+Note:
+
+Definition of a complete binary tree from Wikipedia:
+In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.
+
+Example:
+
+Input: 
+    1
+   / \
+  2   3
+ / \  /
+4  5 6
+
+Output: 6
+
+*/
+
+class Solution {
+public:
+    int countNodes(TreeNode* root) {
+        if(root == NULL) return 0;
+        return 1 + countNodes(root->left) + countNodes(root->right);
+    }
+};

24.cpp

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+/*
+
+Unique Binary Search Trees
+--------------------------
+
+Given n, how many structurally unique BST's (binary search trees) that store values 1 ... n?
+
+Example:
+
+Input: 3
+Output: 5
+Explanation:
+Given n = 3, there are a total of 5 unique BST's:
+
+   1         3     3      2      1
+    \       /     /      / \      \
+     3     2     1      1   3      2
+    /     /       \                 \
+   2     1         2                 3
+
+*/
+
+class Solution {
+public:
+    int rec(int n, map<int,int> &dp){
+        if(n==0){
+            dp[0] = 1;
+            return 1;
+        }
+        if(dp.find(n)!=dp.end())
+            return dp[n];
+        int sum = 0;
+        for(int k=1;k<=n;k++)
+            sum += rec(n-k,dp)*rec(k-1,dp);
+        dp[n] = sum;
+        return sum;
+    }
+    int numTrees(int n) {
+        map<int,int> dp;
+        return rec(n,dp);
+    }
+};

25.cpp

@@ -0,0 +1,36 @@
+/*
+
+Find the Duplicate Number
+-------------------------
+
+Given an array nums containing n + 1 integers where each integer is between 1 and n (inclusive), prove that at least one duplicate number must exist. Assume that there is only one duplicate number, find the duplicate one.
+
+Example 1:
+
+Input: [1,3,4,2,2]
+Output: 2
+Example 2:
+
+Input: [3,1,3,4,2]
+Output: 3
+Note:
+
+You must not modify the array (assume the array is read only).
+You must use only constant, O(1) extra space.
+Your runtime complexity should be less than O(n2).
+There is only one duplicate number in the array, but it could be repeated more than once.
+
+*/
+
+class Solution {
+public:
+    int findDuplicate(vector<int>& nums) {
+        sort(nums.begin(), nums.end());
+        for (int i = 1; i < nums.size(); i++) {
+            if (nums[i] == nums[i-1]) {
+                return nums[i];
+            }
+        }
+        return -1;
+    }
+};

README.md

@@ -23,4 +23,7 @@
 |  19 |   Longest Duplicate Substring   | [Link](https://github.com/ishpreet-singh/leetcode-june-challenge/blob/master/19.cpp) |
 |  20 |       Permutation Sequence      | [Link](https://github.com/ishpreet-singh/leetcode-june-challenge/blob/master/20.cpp) |
 |  21 |           Dungeon Game          | [Link](https://github.com/ishpreet-singh/leetcode-june-challenge/blob/master/21.cpp) |
-|  22 |         Single Number II        | [Link](https://github.com/ishpreet-singh/leetcode-june-challenge/blob/master/22.cpp) |
+|  22 |         Single Number II        | [Link](https://github.com/ishpreet-singh/leetcode-june-challenge/blob/master/22.cpp) |
+|  23 |    Count Complete Tree Nodes    | [Link](https://github.com/ishpreet-singh/leetcode-june-challenge/blob/master/23.cpp) |
+|  24 |    Unique Binary Search Trees   | [Link](https://github.com/ishpreet-singh/leetcode-june-challenge/blob/master/24.cpp) |
+|  25 |    Find the Duplicate Number    | [Link](https://github.com/ishpreet-singh/leetcode-june-challenge/blob/master/25.cpp) |