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Subarrays with K Different Integers in C++
Suppose we have an array A of positive integers, we can call a good subarray (contiguous) of A, if the number of different integers in that subarray is exactly K. So, if the array is like [1,2,3,1,2] has 3 different integers: 1, 2, and 3. We have to find the number of good subarrays of A.
So, if the input is like [1,2,3,1,4] and K = 3, then the output will be 4, as it can form three subarrays with exactly four distinct integers, these are [1,2,3], [1,2,3,1], [2,3,1], [3,1,4].
To solve this, we will follow these steps −
Define a function atMost(), this will take an array a and variable k,
Define one set current
j := 0, ans := 0, n := size of a
Define one map m
for initialize i := 0, when i < size of a, update (increase i by 1), do −
if m[a[i]] is zero, increase m[a[i]] by 1 then −
while k < 0, do −
if decrease m[a[j]] by 1 and m[a[i]] is zero, then −
(increase k by 1)
(increase j by 1)
x := ((i - j) + 1)
ans := ans + x
return ans
From the main method do the following −
return atMost(a, k) - atMost(a, k - 1);
Let us see the following implementation to get better understanding −
Example
#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
int subarraysWithKDistinct(vector<int>& a, int k) {
return atMost(a, k) - atMost(a, k - 1);
}
int atMost(vector <int>& a, int k){
set <int> current;
int j = 0;
int ans = 0;
int n = a.size();
unordered_map <int, int> m;
for(int i = 0; i < a.size(); i++){
if(!m[a[i]]++) k--;
while(k < 0){
if(!--m[a[j]])
k++;
j++;
}
int x = ((i - j) + 1);
ans += x;
}
return ans;
}
};
main(){
Solution ob;
vector<int> v = {1,2,3,1,4};
cout << (ob.subarraysWithKDistinct(v, 3));
}Input
{1,2,3,1,4}, 3Output
4
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