diff --git a/README.md b/README.md index c58a49802..b50f60137 100644 --- a/README.md +++ b/README.md @@ -18,6 +18,7 @@ LeetCode |983|[Minimum Cost For Tickets](https://leetcode.com/problems/minimum-cost-for-tickets/) | [C++](./algorithms/cpp/minimumCostForTickets/MinimumCostForTickets.cpp)|Medium| |981|[Time Based Key-Value Store](https://leetcode.com/problems/time-based-key-value-store/) | [C++](./algorithms/cpp/timeBasedKeyValueStore/TimeBasedKeyValueStore.cpp)|Medium| |980|[Unique Paths III](https://leetcode.com/problems/unique-paths-iii/) | [C++](./algorithms/cpp/uniquePaths/UniquePaths.III.cpp)|Hard| +|979|[Distribute Coins in Binary Tree](https://leetcode.com/problems/distribute-coins-in-binary-tree/) | [C++](./algorithms/cpp/distributeCoinsInBinaryTree/DistributeCoinsInBinaryTree.cpp)|Medium| |978|[Longest Turbulent Subarray](https://leetcode.com/problems/longest-turbulent-subarray/) | [C++](./algorithms/cpp/longestTurbulentSubarray/LongestTurbulentSubarray.cpp),[Python](./algorithms/python/LongestTurbulentSubarray/maxTurbulenceSize.py)|Medium| |977|[Squares of a Sorted Array](https://leetcode.com/problems/squares-of-a-sorted-array/) | [C++](./algorithms/cpp/squaresOfASortedArray/SquaresOfASortedArray.cpp), [Python](./algorithms/python/SquaresOfSortedArray/sortedSquares.py)|Easy| |976|[Largest Perimeter Triangle](https://leetcode.com/problems/largest-perimeter-triangle/) | [Python](./algorithms/python/LargestPerimeterTriangle/largestPerimeter.py)|Easy| diff --git a/algorithms/cpp/distributeCoinsInBinaryTree/DistributeCoinsInBinaryTree.cpp b/algorithms/cpp/distributeCoinsInBinaryTree/DistributeCoinsInBinaryTree.cpp new file mode 100644 index 000000000..09f6a7f71 --- /dev/null +++ b/algorithms/cpp/distributeCoinsInBinaryTree/DistributeCoinsInBinaryTree.cpp @@ -0,0 +1,90 @@ +// Source : https://leetcode.com/problems/distribute-coins-in-binary-tree/ +// Author : Hao Chen +// Date : 2019-03-29 + +/***************************************************************************************************** + * + * Given the root of a binary tree with N nodes, each node in the tree has node.val coins, and there + * are N coins total. + * + * In one move, we may choose two adjacent nodes and move one coin from one node to another. (The + * move may be from parent to child, or from child to parent.) + * + * Return the number of moves required to make every node have exactly one coin. + * + * Example 1: + * + * Input: [3,0,0] + * Output: 2 + * Explanation: From the root of the tree, we move one coin to its left child, and one coin to its + * right child. + * + * Example 2: + * + * Input: [0,3,0] + * Output: 3 + * Explanation: From the left child of the root, we move two coins to the root [taking two moves]. + * Then, we move one coin from the root of the tree to the right child. + * + * Example 3: + * + * Input: [1,0,2] + * Output: 2 + * + * Example 4: + * + * Input: [1,0,0,null,3] + * Output: 4 + * + * Note: + * + * 1<= N <= 100 + * 0 <= node.val <= N + * + ******************************************************************************************************/ + +/** + * 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 distributeCoins(TreeNode* root) { + int result = 0; + dfs(root, result); + return result; + } + + // + // if a node has 0 coin, which means one move from its parent. + // 1 coin, which means zero move from its parent. + // N coins, which means N-1 moves to its parent. + // + // So, we can simply know, the movement = coins -1. + // - negative number means the the coins needs be moved in. + // - positive number means the the coins nees be moved out. + // + // A node needs to consider the movement requests from both its left side and right side. + // and need to calculate the coins after left and right movement. + // + // So, the node coins = my conins - the coins move out + the coins move in. + // + // Then we can have to code as below. + // + int dfs(TreeNode* root, int& result) { + if (root == NULL) return 0; + + int left_move = dfs(root->left, result); + int right_move = dfs(root->right, result); + result += (abs(left_move) + abs(right_move)); + + // the coin after movement: coins = root->val +left_move + right_move + // the movement needs: movement = coins - 1 + return root->val + left_move + right_move - 1; + } +};