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HasPathSum112.java
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HasPathSum112.java
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package Leetcode;
import java.util.LinkedList;
import java.util.Queue;
public class HasPathSum112 {
/*Method : Recursive, Time: O(N), Space:O(H)**/
public boolean hasPathSum(TreeNode root, int targetSum) {
if(root == null) { // root 为空的时候,表示没有path, 所以返回false
return false;
}
if(root.left == null && root.right == null) { //左右节点都为空,才行
return root.val == targetSum;
}
return hasPathSum(root.left, targetSum-root.val) || hasPathSum(root.right, targetSum - root.val);
}
/**Method2: BFS; Time: O(N), Space: O(H) **/
/**思路:
两个栈,一个保存将要遍历的节点,一个保存根节点到这些节点的路径和。
**/
public boolean hasPathSum2(TreeNode root, int targetSum) {
if(root == null) {
return false;
}
Queue<TreeNode> qNode = new LinkedList<>();
Queue<Integer> qSum = new LinkedList<>();
qNode.offer(root);
qSum.offer(root.val);
while(!qNode.isEmpty()) {
TreeNode node = qNode.poll();
int temp = qSum.poll();
if(node.left == null && node.right == null) {
if(temp == targetSum) {
return true;
}
continue;
}
if(node.left != null) {
qNode.offer(node.left);
qSum.offer(temp + node.left.val);
}
if(node.right != null) {
qNode.offer(node.right);
qSum.offer(temp + node.right.val);
}
}
return false;
}
//Definition for a binary tree node.
public class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode() {}
TreeNode(int val) { this.val = val; }
TreeNode(int val, TreeNode left, TreeNode right) {
this.val = val;
this.left = left;
this.right = right;
}
}
}