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Data Stream as Disjoint Intervals in C++
Suppose we have a data stream input of integers, these are like a1, a2, ..., an, ..., we have to summarize the numbers seen so far as a list of disjoint intervals. For example, suppose the input integers are 1, 3, 8, 2, 7, ..., then the summary will be −
[1,1]
[1, 1], [3, 3]
[1, 1], [3, 3], [8, 8]
[1, 3], [8, 8]
[1, 3], [7, 8].
To solve this, we will follow these steps −
Make a set called nums
in the initializer, set low := -inf and high := inf
From the addNum method that takes num as input, insert num into the set nums
From the get interval method, do following −
Define one 2D array ret
it := start element of set nums
while it is in the set, do −
x := value of it
if ret is empty or element at index 1 of last element of ret + 1 < x, then,
insert pair { x, x } at the end of ret
Otherwise
increase the element present at index 1 of last element of ret by 1
it to next element
return ret
Example
Let us see the following implementation to get a better understanding −
#include <bits/stdc++.h<
using namespace std;
void print_vector(vector<vector<auto> > v){
cout << "[";
for(int i = 0; i<v.size(); i++){
cout << "[";
for(int j = 0; j <v[i].size(); j++){
cout << v[i][j] << ", ";
}
cout << "],";
}
cout << "]"<<endl;
}
class SummaryRanges {
public:
set <int> nums;
int low, high;
SummaryRanges() {
low = INT_MAX;
high = INT_MIN;
}
void addNum(int val) {
nums.insert(val);
}
vector<vector<int>> getIntervals() {
vector < vector <int> > ret;
set <int> :: iterator it = nums.begin();
while(it != nums.end()){
int x = *it;
if(ret.empty() || ret.back()[1] + 1 < x){
ret.push_back({x, x});
} else {
ret.back()[1]++;
}
it++;
}
return ret;
}
};
main(){
SummaryRanges ob;
ob.addNum(1);
print_vector(ob.getIntervals());
ob.addNum(3);
print_vector(ob.getIntervals());
ob.addNum(8);
print_vector(ob.getIntervals());
ob.addNum(2);
print_vector(ob.getIntervals());
ob.addNum(7);
print_vector(ob.getIntervals());
}Input
Initialize the class, then insert one element at a time and see the intervals. So the elements are [1,3,8,2,7]
Output
[[1, 1, ],] [[1, 1, ],[3, 3, ],] [[1, 1, ],[3, 3, ],[8, 8, ],] [[1, 3, ],[8, 8, ],] [[1, 3, ],[7, 8, ],]
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