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tree_diameter_dp.cpp
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tree_diameter_dp.cpp
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#include <bits/stdc++.h>
using namespace std;
vector<vector<int>> g;
vector<int> h;
int n;
// finding height of each node.
// Argument p here is the parent of current node
int height(int curr, int p)
{
for (auto it : g[curr])
{
if (it == p)
{
continue;
}
h[curr] = max(h[curr], height(it, curr));
}
h[curr] += 1;
return h[curr];
}
// finding diameter
int diameter(int curr, int p)
{
int mx1, mx2, mx_subtree;
mx1 = mx2 = mx_subtree = INT_MIN;
for (auto it : g[curr])
{
if (it == p)
{
continue;
}
if (mx1 < h[it])
{
mx2 = mx1;
mx1 = h[it];
}
else
{
mx2 = h[it];
}
}
for (auto it : g[curr])
{
if (it == p)
{
continue;
}
mx_subtree = max(mx_subtree, diameter(it, curr));
}
// diameter will be max of diameter in the subtrees or if it passes
// through current node then it will be the sum of maximum heights
// of any two of its children + 1(1 for current node).
return max(mx_subtree, mx1 + mx2 + 1);
}
int main()
{
cin >> n;
g.resize(n + 1);
h.resize(n + 1, 0);
for (int i = 0, u, v; i < n - 1; i++)
{
cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
// choosing root to be 1.
height(1, -1);
cout << diameter(1, -1);
return 0;
}