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LC112_PathSum.java

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import java.util.ArrayList;

import java.util.List;

import java.util.TreeMap;

/**

*

* Remove all elements from a linked list of integers that have value val.

*

* Example:

*

* Input: 1->2->6->3->4->5->6, val = 6

* Output: 1->2->3->4->5

*

* @authorLiu.3502

* @created2018-01-31 下午6:45

*/

public class LC112_PathSum {

public static class ListNode {

int val;

ListNode next;

ListNode(int x) { val = x; }

}

public static void main(String[] args) {

ListNode root = new ListNode(0);

ListNode ans = hasPathSum(root,0);

System.out.println(ans);

}

//O(N)

public boolean hasPathSum(TreeNode root, int sum) {

//sanity check

if(root == null){

return false;

}

returen pathSum(root, 0, sum);

}

public boolean pathSum(TreeNode root, int cur, int sum){

if(root == null){

return cur == sum;

}

if(pathSum(root.left, cur + root.val, sum) || pathSum(root.right, cur + root.val, sum)){

return true;

}

return false;

}

//切记 sum == 0 时候 root == null 不能判断

//必须要把base case改好

public boolean hasPathSum(TreeNode root, int sum) {

if(root == null) return false;

if(root.left == null && root.right == null && root.val == sum){

return true;

}

return hasPathSum(root.left, sum - root.val)|| hasPathSum(root.right, sum - root.val);

}

}