描述

【算法】路径总和112

路径总和112II

分析

实现

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import java.util.List;
import java.util.LinkedList;

//112. 路径总和
public class PathSum112 {
	public static void main(String[] args){
		

		TreeNode root = MyUtils.buildTree(
			new Integer[]{5,4,8,11,null,13,4,7,2,null,null,null,1}
		);
		if (new Solution().hasPathSum(root, 22)) {
			System.out.println("Yes");
		}else{
			System.out.println("No");
		}
	}
}

class Solution {
	//递归实现
    public boolean hasPathSum(TreeNode root, int targetSum) {
    	if (root == null ) return false;
    	//叶子节点
    	if (root.left == null && root.right == null) return root.val == targetSum;
    	//中间
    	return hasPathSum(root.left,targetSum - root.val) || hasPathSum(root.right, targetSum - root.val);
    }
}
//路径总和II
class Solution2 {
	List<List<Integer>> res;
	LinkedList<Integer> path;
    public List<List<Integer>> pathSum(TreeNode root, int targetSum) {
    	
    	res = new LinkedList<>();
    	path = new LinkedList<>();
    	travesal(root,targetSum);
    	return res;
    }
    private void travesal(TreeNode root, int count){
    	if (root == null) {
    		return;
    	}
    	path.offer(root.val);
    	count -= root.val;

    	//叶子节点
    	if (root.left == null && root.right == null && count == 0)
    		res.add(new LinkedList<>(path));
    	travesal(root.left, count);
    	travesal(root.right, count);
    	path.removeLast();//回溯
    }
}


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

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

class MyUtils {
	/**
	 *二叉树的构建
	 * int[] -> 二叉树
	 */
	public static TreeNode buildTree(Integer[] arr) {
        return buildTreeHelper(arr, 0);
    }

    public static TreeNode buildTreeHelper(Integer[] arr, Integer index) {
        if (index >= arr.length || arr[index] == null) {
            return null;
        }

        TreeNode node = new TreeNode(arr[index]);

        node.left = buildTreeHelper(arr, 2 * index + 1);
        node.right = buildTreeHelper(arr, 2 * index + 2);

        return node;
    }
}

总结