[LeetCode]Path Sum

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.

题挺水的,不过刚开始一直wa了几次,发觉基础真的好重要,我把leaf这个概念弄混了.我刚开始只是判断有一条路某时刻满足条件就判断true了，结果就wa了好几次.

leaf的定义是左右子节点都为空！！！

code

public class Solution {

public boolean hasPathSum( TreeNode root, int sum ) {
if( root != null ) {
sum -= root.val;
if( sum == 0 && root.left == null && root.right == null )
return true;
else
return hasPathSum( root.left, sum ) || hasPathSum( root.right, sum );
} else
return false;
}

public static void main( String[] args ) {
Solution s = new Solution();
TreeNode root = new TreeNode( 5 );
root.left = new TreeNode( 4 );
root.left.left = new TreeNode( 11 );
root.left.left.left = new TreeNode( 7 );
root.left.left.right = new TreeNode( 2 );
root.right = new TreeNode( 8 );
root.right.left = new TreeNode( 13 );
root.right.right = new TreeNode( 4 );
root.right.right.right = new TreeNode( 1 );

// root.left = new TreeNode( 1 );

System.out.println( s.hasPathSum( root, 9 ) );
}

}

class TreeNode {

int val;

TreeNode left;

TreeNode right;

TreeNode( int x ) {
val = x;
}
}