LeetCode 437 Path Sum III DFS

阿新 • • 發佈：2022-05-20

Given the root of a binary tree and an integer targetSum, return the number of paths where the sum of the values along the path equals targetSum.

The path does not need to start or end at the root or a leaf, but it must go downwards (i.e., traveling only from parent nodes to child nodes).

Solution

和以往的題目不同：只需要找到樹中的一條路徑即可。因此一個相對暴力的做法就是以每個節點為 \(root\)

進行求解這顆樹下的方案數，那麼遞迴來看的話：

\[\text{dfs}(root)+\text{pathSum}(root.left,targetSum)+\text{pathSum}(root.left,targetSum) \]

現在對於每棵樹，我們用 \(dfs\) 來遞迴答案

點選檢視程式碼

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
private:
    long long dfs(TreeNode* root, long long prev, int targetSum){
        if(!root) return 0;
        long long cur = prev + root->val;
        return (cur==targetSum) + dfs(root->right, cur, targetSum) + dfs(root->left, cur, targetSum);
    }
public:
    int pathSum(TreeNode* root, int targetSum) {
        if(!root) return 0;
        return dfs(root, 0, targetSum) + pathSum(root->left, targetSum) + pathSum(root->right, targetSum);
    }
};

LeetCode 437 Path Sum III DFS

Given the root of a binary tree and an integer targetSum, return the number of paths where the sum of the values along the path equals targetSum.

437. Path Sum III

You are given a binary tree in which each node contains an integer value. Find the number of paths that sum to a given value.

[LeetCode] 437. Path Sum Ⅲ（路徑和之三）

Difficulty: Medium Related Topics: Tree Link: https://leetcode.com/problems/path-sum-iii/ Description You are given a binary tree in which each node contains an integer value.

leetcode 38:path-sum

題目描述給定一個二叉樹和一個值sum，判斷是否有從根節點到葉子節點的節點值之和等於sum的路徑，例如：給出如下的二叉樹，sum=22，5/ \\48// \\11 13 4/ \\\\721 返回true，因為存在一條路徑5->4->11-&

0437. Path Sum III (M)

Path Sum III (M) 題目 You are given a binary tree in which each node contains an integer value. Find the number of paths that sum to a given value.

LeetCode 437. 路徑總和 III

437. 路徑總和 III Difficulty: 中等給定一個二叉樹，它的每個結點都存放著一個整數值。

LeetCode 437 路徑總和 III

LeetCode 437路徑總和 III 1. 題目給定一個二叉樹的根節點 root ，和一個整數 targetSum ，求該二叉樹裡節點值之和等於 targetSum 的路徑的數目。

Leetcode 216 Combination Sum III

https://leetcode.cn/problems/combination-sum-iii/ 遞迴標準題目先寫遞迴函式，一邊寫一邊看缺少什麼輸入。

【刷題-LeetCode】216. Combination Sum III

Combination Sum III Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers.

leetcode 37：path-sum-ii

題目描述給定一個二叉樹和一個值sum\\ sumsum，請找出所有的根節點到葉子節點的節點值之和等於sum\\ sumsum 的路徑，例如：給出如下的二叉樹，sum=22\\ sum=22sum=22，

[LeetCode] 1289. Minimum Falling Path Sum II 下降路徑最小和之二

Given an n x n integer matrix grid, return the minimum sum of a falling path with non-zero shifts.

LeetCode 0064 Minimum Path Sum

原題傳送門 1. 題目描述 2. Solution 1 1、思路分析 1. 狀態定義 minSum[i][j] 表示到達grid[i][j]是的路徑最小和

LeetCode 124. Binary Tree Maximum Path Sum

題目連結：https://leetcode.com/problems/binary-tree-maximum-path-sum/ 題意：已知一棵二叉樹每個節點的權值，求一條權值和最大的路徑，路徑至少包含一個節點，可以不包括根節點。

LeetCode 0124 Binary Tree Maximum Path Sum

原題傳送門 1. 題目描述 2. Solution 1 1、思路分析遞迴。先計算從給定結點的最大貢獻值，具體地，就是在以該結點為根結點的子樹中尋找以該結點為起點的一條路徑，使得該路徑上的結點值之和最大。計算方法: 1>

437 路徑總和iii

一、雙遞迴遍歷二叉樹的每一個節點，然後以該節點為dfs的搜尋起點，判斷累加和是否為給定值，進行計數

力扣 64.最小路徑和 Minimum Path Sum

動態規劃題一直是我的弱項，這道題之前應該是遇到過，但那時自己想不出來，就看了看題解，沒有做。今天力扣的每日一題又遇到了，正好做一下。

minimum-path-sum

題目描述給定一個由非負整數填充的m x n的二維陣列，現在要從二維陣列的左上角走到右下角，請找出路徑上的所有數字之和最小的路徑。注意：你每次只能向下或向右移動。

Leetcode: 220. Contains Duplicate III

Description Given an array of integers, find out whether there are two distinct indices i and j in the array such that the absolute difference between nums[i] and nums[j] is at most t and the absolute

[LeetCode] 499. The Maze III

There is aballin a maze with empty spaces and walls. The ball can go through empty spaces by rollingup(u),down(d),left(l) orright(r), but it won\'t stop rolling until hitting a wall. When the ball sto

LeetCode 337. House Robber III 打家劫舍

第一次用結構體代替dp陣列，這個題沒有標明樹的深度，用陣列存二叉樹會爆記憶體。

LeetCode 437 Path Sum III DFS

Solution

相關推薦