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Largest subarray having sum greater than k in C++
In this tutorial, we are going to write a program that finds the largest subarray have sum greater than k.
Let's see the steps to solve the problem.
- Initialise the array.
- Iterate over the array and store sum at each index in a vector along with the index.
- Sort the above sums based on sum and index.
- Initialise an array to store the indexes.
- Write a loop that iterates till n.
- Update the values with min index of above indexes array and previous sums array index.
- Initialise sum to 0.
- Write a loop that iterates till n.
- Add current element to sum.
- If the sum is greater than k.
- The maximum subarray length is i + 1.
- Else the maximum subarray length is
- Find the index from the previous sums using binary search.
- The sum that is less than sum - k - 1 is the element index we want.
Example
Let's see the code.
#include <bits/stdc++.h>
using namespace std;
bool compare(const pair<int, int>& a, const pair<int, int>& b) {
if (a.first == b.first) {
return a.second < b.second;
}
return a.first < b.first;
}
int findIndex(vector<pair<int, int> >& previousSums, int n, int val) {
int start = 0;
int end = n - 1;
int mid, result = -1;
while (start <= end) {
mid = (start + end) / 2;
if (previousSums[mid].first <= val) {
result = mid;
start = mid + 1;
}else {
end = mid - 1;
}
}
return result;
}
int getLargestSubArray(int arr[], int n, int k) {
int maxLength = 0;
vector<pair<int, int> > previousSums;
int sum = 0, minIndexes[n];
for (int i = 0; i < n; i++) {
sum = sum + arr[i];
previousSums.push_back({ sum, i });
}
sort(previousSums.begin(), previousSums.end(), compare);
minIndexes[0] = previousSums[0].second;
for (int i = 1; i < n; i++) {
minIndexes[i] = min(minIndexes[i - 1], previousSums[i].second);
}
sum = 0;
for (int i = 0; i < n; i++) {
sum = sum + arr[i];
if (sum > k) {
maxLength = i + 1;
}else {
int ind = findIndex(previousSums, n, sum - k - 1);
if (ind != -1 && minIndexes[ind] < i) {
maxLength = max(maxLength, i - minIndexes[ind]);
}
}
}
return maxLength;
}
int main() {
int arr[] = { 5, 3, -3, 2, 4, 7 };
int k = 5, n = 6;
cout << getLargestSubArray(arr, n, k) << endl;
return 0;
}Output
If you run the above code, then you will get the following result.
6
Conclusion
If you have any queries in the tutorial, mention them in the comment section.
Updated on: 09-Apr-2021
275 Views
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