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Problem Path Sum II

Problem Description: Given a binary tree and a sum, find all root-to-leaf paths where each path‘s sum equals the given sum.

Solution: 递归。

 1 public List<List<Integer>> pathSum(TreeNode root, int sum) { 2         List<List<Integer>> list = new ArrayList<List<Integer>>(); 3         if (root == null) return list; 4         List<Integer> tmp = new ArrayList<Integer>(); 5         path(root, sum, list, tmp); 6         return list; 7     } 8     public void path(TreeNode root, int sum, List<List<Integer>> list, List<Integer> tmp) { 9         if (root == null) return;10         tmp.add(root.val);11         int leftsum = sum - root.val;12 13         if (leftsum == 0 && root.left == null && root.right == null) {14             list.add(new ArrayList<Integer>(tmp));15         }16         path(root.left, leftsum, list, tmp);17         path(root.right, leftsum, list, tmp);18 19         tmp.remove(tmp.size() - 1);20     }