LeetCode-Alg-437-Path Sum III

LeetCode-Alg-437-Path Sum III

Posted by Jae on May 6, 2019

1、题目

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.

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

The tree has no more than 1,000 nodes and the values are in the range -1,000,000 to 1,000,000.

Example:

root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8

10
/  \
5   -3
/ \    \
3   2   11
/ \   \
3  -2   1

Return 3. The paths that sum to 8 are:

1.  5 -> 3
2.  5 -> 2 -> 1
3. -3 -> 11


4、实现

public class Solution{ private int count=0; public int pathSum(TreeNode root, int sum) {

    findPath(root, sum);
return count;
}

// sum为路径和
private void findPath(TreeNode root, int sum){
if (root == null){
return;
}
// 以当前节点为根节点往下寻找
bfs(root, 0, sum);
// 去左子树继续寻找
findPath(root.left, sum);
// 去右子树继续寻找
findPath(root.right, sum);
}

// 深度优先遍历，并计算每次经过的路径的和
public void bfs(TreeNode root, int sum, int target){
if (root == null){
return;
}
sum += root.val;
if (sum == target){
count++;
}
bfs(root.left, sum, target);
bfs(root.right, sum, target);
sum -= root.val;
} }