112. Path Sum

原题链接：https://leetcode.com/problems/path-sum/description/
二叉树相关问题，直接深度优先搜索走一波：

/**
 * Created by clearbug on 2018/2/26.
 */
public class Solution {

    static class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        public TreeNode(int val) {
            this.val = val;
        }
    }

    public static void main(String[] args) {
        Solution s = new Solution();

        // test1
        TreeNode root = new TreeNode(3);
        root.left = new TreeNode(9);
        root.left.left = new TreeNode(33);
        root.right = new TreeNode(20);
        root.right.left = new TreeNode(15);
        root.right.right = new TreeNode(7);
        System.out.println(s.hasPathSum(root, 45));
        System.out.println(s.hasPathSum(root, 38));
        System.out.println(s.hasPathSum(root, 30));
        System.out.println(s.hasPathSum(root, 46));
        System.out.println(s.hasPathSum(root, 20));
    }

    public boolean hasPathSum(TreeNode root, int sum) {
        if (root == null) {
            return false;
        }
        return dfs(root, sum, 0);
    }

    private boolean dfs(TreeNode node, int sum, int currentSum) {
        currentSum += node.val;
        if (node.left == null && node.right == null) {
            if (currentSum == sum) {
                return true;
            }
        } else {
            if (node.left != null) {
                if (dfs(node.left, sum, currentSum)) {
                    return true;
                }
            }
            if (node.right != null) {
                if (dfs(node.right, sum, currentSum)) {
                    return true;
                }
            }
        }
        return false;
    }

}