Day 7 Q 2

Author: Apoorv012

Problems/Binary-Search/Day-07/Apoorv012/Solution2.cpp

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+/*
+
+Link: https://codeforces.com/contest/1777/submission/356094799
+
+Approach:
+we dont care about duplicates, so keep unique
+it is a sliding window problem, we sort them based on their smartness, and have a precomuted array of factors
+we go through each one of them, and see if we cover all the topics... 
+if we do, we start removing the students to the left side... if less, then add from right side
+
+*/
+
+#include <bits/stdc++.h>
+using namespace std;
+
+const int MAX_N = 1e5 + 5;
+vector<vector<int>> factors(MAX_N);
+
+void generateFactors() {
+    for (int x = 2; x < MAX_N; x++) {
+        for (int y = x; y < MAX_N; y += x) {
+            factors[y].push_back(x);
+        }
+    }
+}
+
+void solve() {
+    int n, m;
+    cin >> n >> m;
+    vector<int> a(n);
+    for (auto &x: a) cin >> x;
+
+    vector<int> curr(m+1);
+    int cnt = 0;
+
+    if (m == 1) {
+        cout << 0 << endl;
+        return;
+    }
+
+    sort(a.begin(), a.end());
+    // cout << "sorted a\n";
+    auto it = std::unique(a.begin(), a.end());
+    a.erase(it, a.end());
+
+    n = a.size();
+
+    int l = 0, r = 0, best = INT_MAX;
+    while (r < n) {
+        // cout << "l, r: " << l << " " << r << endl;
+        for (auto factor: factors[a[r]]) {
+            if (factor > m) break;
+            if (curr[factor] == 0) cnt++;
+            curr[factor]++;
+        }
+        while (cnt == m-1) {
+            best = min(best, a[r] - a[l]);
+            for (auto factor: factors[a[l]]) {
+                if (factor > m) break;
+                curr[factor]--;
+                if (curr[factor] == 0) cnt--;
+            }
+            l++;
+        }
+        r++;
+    }
+
+    // for (auto x: a) cout << x << " ";
+    cout << (best == INT_MAX ? -1 : best) << endl;
+}
+
+int main() {
+    generateFactors();
+    // cout << "generated factors\n";
+
+    int t;
+    cin >> t;
+    while (t--) {
+        // cout << "t: " << t << endl;
+        solve();
+    }
+}