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PathSum.java
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53 lines (46 loc) · 1.2 KB
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package algorithm.lc;
/**
* 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.
*
*/
public class PathSum {
public class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) {
val = x;
}
}
// O(1) space, O(n) time
public class Solution {
public boolean hasPathSum(TreeNode root, int sum) {
// Note: The Solution object is instantiated only once and is reused by each test case.
return hasPath(root, sum, 0);
}
private boolean hasPath(TreeNode node, int sum, int curSum) {
if (node == null) {
return false;
}
if (node.left == null && node.right == null) {
return curSum + node.val == sum;
} else {
return hasPath(node.left, sum, curSum + node.val) || hasPath(node.right, sum, curSum + node.val);
}
}
}
}