Sync LeetCode submission Runtime - 590 ms (24.56%), Memory - 264.8 MB (12.28%)

Author: koralkulacoglu

LeetCode/2364-longest-path-with-different-adjacent-characters/README.md

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+<p>You are given a <strong>tree</strong> (i.e. a connected, undirected graph that has no cycles) <strong>rooted</strong> at node <code>0</code> consisting of <code>n</code> nodes numbered from <code>0</code> to <code>n - 1</code>. The tree is represented by a <strong>0-indexed</strong> array <code>parent</code> of size <code>n</code>, where <code>parent[i]</code> is the parent of node <code>i</code>. Since node <code>0</code> is the root, <code>parent[0] == -1</code>.</p>
+
+<p>You are also given a string <code>s</code> of length <code>n</code>, where <code>s[i]</code> is the character assigned to node <code>i</code>.</p>
+
+<p>Return <em>the length of the <strong>longest path</strong> in the tree such that no pair of <strong>adjacent</strong> nodes on the path have the same character assigned to them.</em></p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2022/03/25/testingdrawio.png" style="width: 201px; height: 241px;" />
+<pre>
+<strong>Input:</strong> parent = [-1,0,0,1,1,2], s = &quot;abacbe&quot;
+<strong>Output:</strong> 3
+<strong>Explanation:</strong> The longest path where each two adjacent nodes have different characters in the tree is the path: 0 -&gt; 1 -&gt; 3. The length of this path is 3, so 3 is returned.
+It can be proven that there is no longer path that satisfies the conditions. 
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2022/03/25/graph2drawio.png" style="width: 201px; height: 221px;" />
+<pre>
+<strong>Input:</strong> parent = [-1,0,0,0], s = &quot;aabc&quot;
+<strong>Output:</strong> 3
+<strong>Explanation:</strong> The longest path where each two adjacent nodes have different characters is the path: 2 -&gt; 0 -&gt; 3. The length of this path is 3, so 3 is returned.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>n == parent.length == s.length</code></li>
+	<li><code>1 &lt;= n &lt;= 10<sup>5</sup></code></li>
+	<li><code>0 &lt;= parent[i] &lt;= n - 1</code> for all <code>i &gt;= 1</code></li>
+	<li><code>parent[0] == -1</code></li>
+	<li><code>parent</code> represents a valid tree.</li>
+	<li><code>s</code> consists of only lowercase English letters.</li>
+</ul>

LeetCode/2364-longest-path-with-different-adjacent-characters/solution.cpp

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+class Solution {
+public:
+    int longestPath(vector<int>& parent, string s) {
+        int n = parent.size();
+        unordered_map<int, vector<int>> tree;
+        for (int i=0; i<n; i++) tree[parent[i]].push_back(i);
+
+        int ans = 1;
+
+        auto dfs = [&](auto&& self, int node) -> pair<char, int> {
+            vector<pair<char, int>> paths;
+            for (int neigh : tree[node]) paths.push_back(self(self, neigh));
+
+            int maxLen = 1;
+            for (auto path : paths) {
+                char prev = path.first;
+                int len = path.second;
+                if (prev == s[node]) continue;
+
+                ans = max(ans, maxLen + len);
+                maxLen = max(maxLen, len + 1);
+            }
+
+            return {s[node], maxLen};
+        };
+
+        dfs(dfs, 0);
+
+        return ans;
+    }
+};