leetcode112路徑總和

使用了遞歸解決。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean hasPathSum(TreeNode root, int sum) {}
        if(root==null){			//如果根節點爲空，則直接返回false
            return false;
        }
        return hasSum(root, sum,root.val);
        
    }
    public static boolean hasSum(TreeNode node,int sum,int currentSum){
        if(currentSum==sum && node.left==null && node.right==null){     //主要針對根節點
            return true;
        }


        ////System.out.println(node.val+"       "+currentSum);
        if(node.left!=null){							//遍歷左子樹
            //System.out.println("leftleft       ");
            currentSum+=node.left.val;
            //System.out.println("current = "+currentSum);
            if(currentSum==sum && node.left.left==null && node.left.right==null){
                return true;
            }else {
                if(hasSum(node.left, sum, currentSum)){
                    return true;
                  }
            }
            currentSum-=node.left.val;				//失敗，還原currentSum
        }

        if(node.right!=null){						//遍歷右子樹
           // System.out.println("rightrightright          ");
            currentSum+=node.right.val;
            //System.out.println("current = "+currentSum);
            if(currentSum==sum && node.right.left==null && node.right.right==null){
                return true;
            }else {
                if( hasSum(node.right, sum, currentSum)){
                    return true;
                }
            }
            currentSum-=node.right.val;
        }


        return false;
    }
}