Leetcode:path Sum III

You are given a binary treeinchwhich each node contains an integer value. Find the number of paths this sum to a given value. The path does not need to start or end on the root or a leaf, but it must go downwards (traveling only fromparent nodes to child nodes). The tree has no more than1, theNodes and the values areinchThe range-1, the, theTo1, the, the. Example:root= [Ten,5,-3,3,2,NULL, One,3,-2,NULL,1], sum =8      Ten/      5-3/ \      3   2    One/ \   3-2   1Return3. The paths, sum to8is :1.5-32.5-2-13. -3- One

Add the prefix sum to the HASHMAP, and check along path if Hashmap.contains (Pathsum+cur.val-target);

My Solution

1 /**2 * Definition for a binary tree node.3 * public class TreeNode {4 * int val;5 * TreeNode left;6 * TreeNode right;7 * TreeNode (int x) {val = x;}8  * }9  */Ten  Public classSolution { One      Public intPathsum (TreeNode root,intsum) { A         if(Root = =NULL)return0; -arraylist<integer> res =NewArraylist<integer>(); -Res.add (0); theHashmap<integer, integer> map =NewHashmap<integer, integer>(); -Map.put (0, 1); -Helper (root, sum, 0, res, map); -         returnRes.get (0); +     } -      +      Public voidHelper (TreeNode cur,intTargetintPathsum, arraylist<integer> Res, Hashmap<integer, integer>map) { A         if(Map.containskey (pathsum+cur.val-target)) { atRes.set (0, res.get (0) + map.get (pathsum+cur.val-target)); -         } -         if(!map.containskey (pathsum+cur.val)) { -Map.put (Pathsum+cur.val, 1); -         } -         ElseMap.put (Pathsum+cur.val, Map.get (pathsum+cur.val) +1); in         if(Cur.left! =NULL) helper (Cur.left, Target, pathsum+Cur.val, res, map); -         if(Cur.right! =NULL) helper (cur.right, Target, pathsum+Cur.val, res, map); toMap.put (Pathsum+cur.val, Map.get (pathsum+cur.val)-1); +     } -}

A more concise solution:

1      Public intPathsum (TreeNode root,intsum) {2Hashmap<integer, integer> presum =NewHashMap ();3Presum.put (0,1);4         returnHelper (root, 0, Sum, presum);5     }6     7      Public intHelper (TreeNode root,intSumintTarget, Hashmap<integer, integer>presum) {8         if(Root = =NULL) {9             return0;Ten         } One          ASum + =Root.val; -         intres = Presum.getordefault (sum-target, 0); -Presum.put (sum, presum.getordefault (sum, 0) + 1); the          -Res + = Helper (root.left, sum, Target, presum) +Helper (root.right, sum, Target, presum); -Presum.put (sum, presum.get (sum)-1); -         returnRes; +}

Leetcode:path Sum III