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Binary Tree Longest Consecutive Sequence II in C++
Suppose we have a binary tree; we have to find the length of the Longest Consecutive Path in that Binary Tree. Here the path can be either increasing or decreasing. So as an example [1,2,3,4] and [4,3,2,1] are both considered as a valid path, but the path [1,2,4,3] is not a valid one.
Otherwise, the path can be in the child-Parent-child sequence, where not necessarily be parent-child order.
So, if the input is like
then the output will be 3 as the longest consecutive path will be like [1, 2, 3] or [3, 2, 1].
To solve this, we will follow these steps −
Define a function solveUtil(), this will take node,
if the node is null, then −
return { 0, 0 }
left = solveUtil(left of node)
left = solveUtil(right of node)
Define one pair temp := {1,1}
if left of node is present and value of left of node is same as value of node + 1, then −
temp.first := maximum of temp.first and 1 + left.first
ans := maximum of ans and temp.first
if right of node is present and value of right of node is same as value of node + 1, then −
temp.first := maximum of temp.first and 1 + right.first
ans := maximum of ans and temp.first
if left of node is present and value of left of node is same as value of node - 1, then −
temp.second := maximum of temp.second and 1 + left.second
ans := maximum of ans and temp.second
if right of node is present and value of right of node is same as value of node - 1, then −
temp.second := maximum of temp.second and 1 + right.second
ans := maximum of ans and temp.second
ans := maximum of { ans and temp.first + temp.second - 1 }
return temp
From the main method do the following −
ans := 0
solveUtil(root)
return ans
Example
Let us see the following implementation to get a better understanding −
#include <bits/stdc++.h>
using namespace std;
class TreeNode{
public:
int val;
TreeNode *left, *right;
TreeNode(int data){
val = data;
left = NULL;
right = NULL;
}
};
class Solution {
public:
int ans = 0;
pair<int, int> solveUtil(TreeNode* node){
if (!node) {
return { 0, 0 };
}
pair<int, int> left = solveUtil(node->left);
pair<int, int> right = solveUtil(node->right);
pair<int, int> temp = { 1, 1 };
if (node->left && node->left->val == node->val + 1) {
temp.first = max(temp.first, 1 + left.first);
ans = max(ans, temp.first);
}
if (node->right && node->right->val == node->val + 1) {
temp.first = max(temp.first, 1 + right.first);
ans = max(ans, temp.first);
}
if (node->left && node->left->val == node->val - 1) {
temp.second = max(temp.second, 1 + left.second);
ans = max(ans, temp.second);
}
if (node->right && node->right->val == node->val - 1) {
temp.second = max(temp.second, 1 + right.second);
ans = max(ans, temp.second);
}
ans = max({ ans, temp.first + temp.second - 1 });
return temp;
}
int longestConsecutive(TreeNode* root){
ans = 0;
solveUtil(root);
return ans;
}
};
main(){
Solution ob;
TreeNode *root = new TreeNode(2);
root->left = new TreeNode(1);
root->right = new TreeNode(3);
cout << (ob.longestConsecutive(root));
}Input
TreeNode *root = new TreeNode(2); root->left = new TreeNode(1); root->right = new TreeNode(3);
Output
3
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