solved q2 of day 4

Author: DoonMad

Problems/Data-structures/Day-04/sol/DoonMad/q002.cpp

@@ -0,0 +1,82 @@
+#include<bits/stdc++.h>
+
+using namespace std;
+#define int long long
+
+// time complexity: O(n*log(n))
+// space complexity: O(n)
+// submission link: https://codeforces.com/problemset/submission/1912/355861913
+
+struct Segment {
+    int cost;  // min cost (-ve elements before +ve gain)
+    int gain; // net gain
+    int idx; // list idx
+    
+    // priority Queue needs to order by cost
+    //priority_queue is a max-heap, so we use > for min-heap behavior
+    bool operator>(const Segment& other) const {
+        return cost > other.cost;
+    }
+};
+
+int solve(){
+    int x, k; cin>>x>>k;
+    
+    vector<vector<Segment>> segments(k);
+
+    for(int i = 0; i < k; i++){
+        int t; cin >> t;
+        int sum = 0;
+        int cost = 0;
+        
+        for(int j = 0; j < t; j++){
+            int val; cin >> val;
+            sum += val;
+            cost = min(cost, sum);
+            
+            // If we found a net positive chunk, save it as a segment
+            if(sum > 0){
+                // If cost is -5, we need at least 5. If cost is 2, we need 0.
+                segments[i].push_back({max(0LL, -cost), sum, i});
+                sum = cost = 0;
+            }
+        }
+    }
+    
+    priority_queue<Segment, vector<Segment>, greater<Segment>> pq;
+    vector<int> ptr(k, 0); // ptrs for each list's current idx
+
+    // add the first segment of each list (if it exists)
+    for(int i = 0; i < k; i++){
+        if(segments[i].size() > 0){
+            pq.push(segments[i][0]);
+        }
+    }
+
+    while(!pq.empty()){
+        Segment best = pq.top();
+        pq.pop();
+        
+        if(x >= best.cost){
+            x += best.gain;
+            int i = best.idx; // mov ptr forward
+            ptr[i]++;
+            if(ptr[i] < segments[i].size()){
+                pq.push(segments[i][ptr[i]]);
+            }
+        }
+        else break;
+    }
+
+    return x;
+}
+
+int32_t main()
+{
+    ios_base::sync_with_stdio(false);
+    cin.tie(NULL);
+
+    cout << solve() << endl;
+
+    return 0;
+}