Number Stream to Intervals - Amazon Top Interview Questions
Problem Statement :
Implement a data structure with the following methods:
StreamSummary() constructs a new instance.
add(int val) adds the number val to the instance.
int[][] get() returns a sorted list of disjoint intervals summarizing the numbers we've seen so far.
Constraints
n ≤ 10,000 where n is the number of calls to add
m ≤ 10,000 where n is the number of calls to get
Example 1
Input
methods = ["constructor", "add", "add", "add", "add", "get"]
arguments = [[], [1], [3], [2], [9], []]`
Output
[None, None, None, None, None, [
[1, 3],
[9, 9]
]]
Explanation
s = StreamSummary()
s.add(1)
s.add(3)
s.add(2)
s.add(9)
s.get() == [[1, 3], [9, 9]]
Example 2
Input
methods = ["constructor", "add", "add", "add", "add", "get"]
arguments = [[], [1], [2], [4], [3], []]`
Output
[None, None, None, None, None, [
[1, 4]
]]
Explanation
s = StreamSummary()
s.add(1)
s.add(2)
s.add(4)
s.add(3)
s.get() == [[1, 4]]
Solution :
Solution in C++ :
class StreamSummary {
public:
map<int, int> s;
unordered_map<int, int> e;
void add(int val) {
if (e.count(val - 1) and s.count(val + 1)) {
int prevstart = e[val - 1];
int nextend = s[val + 1];
s.erase(val + 1);
e.erase(val - 1);
s[prevstart] = nextend;
e[nextend] = prevstart;
} else if (e.count(val - 1)) {
int prevstart = e[val - 1];
e.erase(val - 1);
s[prevstart] = val;
e[val] = prevstart;
} else if (s.count(val + 1)) {
int nextend = s[val + 1];
s.erase(val + 1);
s[val] = nextend;
e[nextend] = val;
} else {
e[val] = val;
s[val] = val;
}
}
vector<vector<int>> get() {
vector<vector<int>> ret;
for (auto [st, en] : s) {
ret.push_back({st, en});
}
return ret;
}
};
Solution in Java :
import java.util.*;
class StreamSummary {
private TreeMap<Integer, Integer> myMap;
public StreamSummary() {
myMap = new TreeMap<>();
}
public void add(int val) {
if (myMap.containsKey(val)) {
// nothing to do. alreayd covered.
return;
}
Integer lower = myMap.lowerKey(val);
if (lower == null) {
// we got a smallest number
caseSmallest(val);
return;
} else {
caseInsertLower(lower, val);
return;
}
}
// we got a smallest number
private void caseSmallest(int key) {
int nextKey = key + 1;
Integer value = myMap.get(nextKey);
if (value != null) {
// we need to merge
// delete the old one first
myMap.remove(nextKey);
myMap.put(key, value);
} else {
// stand-alone key
myMap.put(key, key);
}
}
// lower < newVal
// lower: a key
private void caseInsertLower(int lower, int newVal) {
Integer val = myMap.get(lower);
if (newVal <= val) {
// newVal is already convered
return;
}
Integer higher = myMap.get(newVal + 1);
if ((((val + 1) == newVal)) && (higher != null)) {
// merge both. case: (1,1),(3,3), and we are adding 2, we should have (1,3)
myMap.put(lower, higher);
myMap.remove(newVal + 1);
} else if (((val + 1) == newVal) && (higher == null)) {
// case: (1,1),(4,4) and we are adding 2. we should have (1,2) and (4,4)
myMap.put(lower, newVal);
} else if (higher != null) {
myMap.remove(newVal + 1);
myMap.put(newVal, higher);
} else {
// no need to merge
myMap.put(newVal, newVal);
}
}
public int[][] get() {
int[][] array = new int[myMap.size()][2];
Iterator<Map.Entry<Integer, Integer>> it;
it = myMap.entrySet().iterator();
int count = 0;
while (it.hasNext()) {
Map.Entry<Integer, Integer> en = it.next();
array[count][0] = en.getKey();
array[count][1] = en.getValue();
count++;
}
return (array);
}
}
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