Path Sum leetcode java

本文转载自查看原文 2014-07-31 02:43 2766 leetcode每题整理

题目：

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

For example:
Given the below binary tree and sum = 22,

              5
             / \
            4   8
           /   / \
          11  13  4
         /  \      \
        7    2      1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

题解：

还是对树的操作，递归的解法：

1      public boolean hasPathSum(TreeNode root, int sum) {
2          if(root == null)
3              return false;
4
5         sum -= root.val;
6          if(root.left == null && root.right== null)
7              return sum == 0;
8          else
9              return hasPathSum(root.left,sum) || hasPathSum(root.right,sum);
10     }

非递归的解法（Reference：http://www.programcreek.com/2013/01/leetcode-path-sum/）：

1      public boolean hasPathSum(TreeNode root, int sum) {
2          if(root == null) return false;
3
4         LinkedList<TreeNode> nodes = new LinkedList<TreeNode>();
5         LinkedList<Integer> values = new LinkedList<Integer>();
6
7         nodes.add(root);
8         values.add(root.val);
9
10          while(!nodes.isEmpty()){
11             TreeNode curr = nodes.poll();
12              int sumValue = values.poll();
13
14              if(curr.left == null && curr.right == null && sumValue==sum){
15                  return true;
16             }
17
18              if(curr.left != null){
19                 nodes.add(curr.left);
20                 values.add(sumValue+curr.left.val);
21             }
22
23              if(curr.right != null){
24                 nodes.add(curr.right);
25                 values.add(sumValue+curr.right.val);
26             }
27         }
28
29          return false;
30     }

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