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Author: MathProgrammer

2023/Contests/Div 2/857/Programs/Buying Gifts.cpp

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+#include <iostream>
+#include <vector>
+#include <algorithm>
+#include <set>
+
+using namespace std;
+
+void solve()
+{
+    int no_of_elements;
+    cin >> no_of_elements;
+
+    vector <int> A(no_of_elements + 1), B(no_of_elements + 1);
+    for(int i = 1; i <= no_of_elements; i++)
+    {
+        cin >> A[i] >> B[i];
+    }
+
+    vector <pair <int, int> > prices (no_of_elements + 1);
+    for(int i = 1; i <= no_of_elements; i++)
+    {
+        prices[i].first = A[i];
+        prices[i].second = B[i];
+    }
+
+    sort(prices.begin() + 1, prices.end());
+    reverse(prices.begin() + 1, prices.end());
+
+    vector <int> prefix_max(no_of_elements + 1);
+    for(int i = 1; i <= no_of_elements; i++)
+    {
+        prefix_max[i] = max(prefix_max[i - 1], prices[i].second);
+    }
+
+    const int oo = 2e9 + 9;
+    int answer = oo;
+    set <int> suffix;
+    vector <int> suffix_next_greater(no_of_elements + 1, oo), suffix_next_lesser(no_of_elements + 1, oo);
+    for(int i = no_of_elements; i >= 1; i--)
+    {
+        auto it = suffix.lower_bound(prices[i].first);
+
+        if(it != suffix.end())
+        {
+            suffix_next_greater[i] = *it;
+        }
+
+        if(it != suffix.begin())
+        {
+            it--;
+        }
+        suffix_next_lesser[i] = *it;
+
+        suffix.insert(prices[i].second);
+    }
+
+    for(int i = no_of_elements; i >= 1; i--)
+    {
+        int answer_here = oo;
+
+        if(i > 1)
+        {
+            answer_here = abs(prices[i].first - prefix_max[i - 1]);
+        }
+
+        if(suffix_next_greater[i] >= prefix_max[i - 1])
+        {
+            answer_here = min(answer_here, abs(prices[i].first - suffix_next_greater[i]));
+        }
+
+        if(suffix_next_lesser[i] >= prefix_max[i - 1])
+        {
+            answer_here = min(answer_here, abs(prices[i].first - suffix_next_lesser[i]));
+        }
+
+        answer = min(answer, answer_here);
+    }
+
+    cout << answer << "\n";
+}
+
+int main()
+{
+    int no_of_test_cases;
+    cin >> no_of_test_cases;
+
+    while(no_of_test_cases--)
+        solve();
+
+    return 0;
+}
+
+