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MaxPathSum124.java
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MaxPathSum124.java
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package Leetcode;
public class MaxPathSum124 {
/**Method: Recursion; Time:O(N); Space: O(N) **/
int maxSum = Integer.MIN_VALUE;
public int maxPathSum(TreeNode root) {
maxGain(root);
return maxSum;
}
private int maxGain(TreeNode node) {
if(node == null) {
return 0;
}
int leftGain = Math.max(maxGain(node.left), 0); //maxGain可能有node的和<0,所以要和0取最大值
int rightGain = Math.max(maxGain(node.right), 0);
int pathValue = node.val +leftGain + rightGain;
maxSum = Math.max(pathValue, maxSum);
return node.val + Math.max(leftGain, rightGain);
}
//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;
}
}
}