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118 lines (109 loc) · 3.33 KB
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/*
* 113. Path Sum II
* Target: Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.
* Note: A leaf is a node with no children.
* Difficulty：Medium
* Classification：Tree, DFS
*/
/*
* Solution 1
* 2019-10-29 Runtime: 1 ms
* Algorithm: => Recursion
* Time Complexity: ?, Space Conplexity: O(1)
*/
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public List<List<Integer>> pathSum(TreeNode root, int sum) {
List<List<Integer>> res = new ArrayList<>();
List<Integer> temp = new ArrayList<>();
if (root == null) {
return res;
}
pathSumHelper(root, sum, temp, res);
return res;
}
private void pathSumHelper(TreeNode cur, int sum, List<Integer> temp, List<List<Integer>> res) {
if (cur.left == null && cur.right == null) {
if (cur.val == sum) {
temp.add(cur.val);
res.add(new ArrayList<>(temp));
temp.remove(temp.size() - 1);
}
return;
}
if (cur.right == null) {
temp.add(cur.val);
pathSumHelper(cur.left, sum - cur.val, temp, res);
temp.remove(temp.size() - 1);
return;
}
if (cur.left == null) {
temp.add(cur.val);
pathSumHelper(cur.right, sum - cur.val, temp, res);
temp.remove(temp.size() - 1);
return;
}
temp.add(cur.val);
pathSumHelper(cur.left, sum - cur.val, temp, res);
temp.remove(temp.size() - 1);
temp.add(cur.val);
pathSumHelper(cur.right, sum - cur.val, temp, res);
temp.remove(temp.size() - 1);
return;
}
}
/*
* Solution 2
* 2019-11-01 Runtime: 1 ms
* Algorithm: => DFS
* Time Complexity: ?, Space Conplexity: O(1)
*/
class Solution {
public List<List<Integer>> pathSum(TreeNode root, int sum) {
List<List<Integer>> res = new ArrayList<>();
List<Integer> temp = new ArrayList<>();
if (root == null) {
return res;
}
Stack<TreeNode> stack = new Stack<>();
TreeNode cur = root;
TreeNode pre = null;
int pathSum = 0;
//stack.push(root);
/*int i = 0;*/
while (!stack.isEmpty() || cur != null) {
/*System.out.println("No. " + i);*/
while (cur != null) {
stack.push(cur);
pathSum += cur.val;
temp.add(cur.val);
cur = cur.left;
}
cur = stack.peek();
/*System.out.println(cur.val);*/
if (cur.left == null && cur.right == null && pathSum == sum) {
res.add(new ArrayList<>(temp));
}
if (cur.right == null || cur.right == pre) {
TreeNode popNode = stack.pop();
pathSum -= popNode.val;
temp.remove(temp.size() - 1);
pre = cur;
cur = null;
} else {
cur = cur.right;
/*System.out.println("cur " + cur.val);*/
}
/*i++;*/
}
return res;
}
}