Path Sum II
Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.
For example:
Given the below binary tree and sum = 22
,
5 / 4 8 / / 11 13 4 / / 7 2 5 1
return
[ [5,4,11,2], [5,8,4,5] ]
这个问题需要返回每条满足sum值的所有路径。思路是:后序遍历,回溯时将当前node.val添加到左右子树的结果中。
递归:
List<List<Int>> path_sum_helper(Treenode node, int current_sum, int depth, int sum_aim):
if (node is leaf-node):
r = [[]]
if (current_sum == sum_aim):
r_i = []
r_i[depth] = node.val
r.add(r_i)
return r
else:
r = [[]]
if(node.left != null):
left_ = path_sum_helper(node.left, current_sum + node.left.val, depth + 1, sum_aim)
if (left_ != null):
r = left_;
for(r_ : r):
r_[level] = node.val
// similar for right sub-tree
// need to merge left and right results
return r