Create Parsa and Humungous Tree.cpp

Author: MathProgrammer

2021/Div 2/722/Programs/Parsa and Humungous Tree.cpp

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+#include <iostream>
+#include <vector>
+#include <algorithm>
+
+using namespace std;
+
+const int MAX_N = 1e5 + 5, MAX_ENDS = 2, L = 0, R = 1;
+vector <int> tree[MAX_N];
+long long maximum_at[MAX_N][MAX_ENDS], left_value[MAX_N], right_value[MAX_N];
+
+void initialize(int no_of_vertices)
+{
+    for(int i = 1; i <= no_of_vertices; i++)
+    {
+        tree[i].clear();
+        maximum_at[i][L] = maximum_at[i][R] = 0;
+    }
+}
+
+void dfs(int v, int parent_v)
+{
+    for(int child_v : tree[v])
+    {
+        if(child_v == parent_v)
+        {
+            continue;
+        }
+
+        dfs(child_v, v);
+
+        long long using_left_value_at_child = abs(left_value[v] - left_value[child_v]) + maximum_at[child_v][L];
+        long long using_right_value_at_child = abs(left_value[v] - right_value[child_v]) + maximum_at[child_v][R];
+
+        maximum_at[v][L] += max(using_left_value_at_child, using_right_value_at_child);
+
+        using_left_value_at_child = abs(right_value[v] - left_value[child_v]) + maximum_at[child_v][L];
+        using_right_value_at_child = abs(right_value[v] - right_value[child_v]) + maximum_at[child_v][R];
+
+        maximum_at[v][R] += max(using_left_value_at_child, using_right_value_at_child);
+    }
+
+    /*cout << "At " << v << " L = " << left_value[v] << " Maximum = " << maximum_at[v][L] << "\n";
+    cout << "At " << v << " R = " << right_value[v] << " Maximum = " << maximum_at[v][R] << "\n";*/
+}
+
+void solve()
+{
+    int no_of_vertices;
+    cin >> no_of_vertices;
+
+    initialize(no_of_vertices);
+
+    for(int i = 1; i <= no_of_vertices; i++)
+    {
+        cin >> left_value[i] >> right_value[i];
+    }
+
+    int no_of_edges = no_of_vertices - 1;
+    for(int i = 1; i <= no_of_edges; i++)
+    {
+        int u, v;
+        cin >> u >> v;
+
+        tree[u].push_back(v);
+        tree[v].push_back(u);
+    }
+
+    dfs(1, 0);
+
+    cout << max(maximum_at[1][L], maximum_at[1][R]) << "\n";
+}
+
+int main()
+{
+    ios_base::sync_with_stdio(false);
+    cin.tie(NULL);
+
+    int no_of_test_cases;
+    cin >> no_of_test_cases;
+
+    while(no_of_test_cases--)
+        solve();
+
+    return 0;
+}