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Longest Substring with At Most Two Distinct Characters in C++
Suppose we have a string s; we have to find the length of the longest substring t that has at most 2 distinct characters.
So, if the input is like "eceba", then the output will be 3 as t is "ece" which its length is 3.
To solve this, we will follow these steps −
Define a function lengthOfLongestSubstringKDistinct(), this will take s, k,
ans := 0
Define one map m
n := size of s, x := 0
for initialize j := 0, i := 0, when j < n, update (increase j by 1), do −
(increase m[s[j]] by 1)
if m[s[j]] is same as 1, then −
(increase x by 1)
while (x > k and i <= j), do −
(decrease m[s[i]] by 1)
if m[s[i]] is same as 0, then −
(decrease x by 1)
(increase i by 1)
ans := maximum of ans and j - i + 1
return ans
From the main method do the following
return lengthOfLongestSubstringKDistinct(s, 2)
Example
Let us see the following implementation to get better understanding −
#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
int lengthOfLongestSubstringKDistinct(string s, int k){
int ans = 0;
unordered_map<char, int> m;
int n = s.size();
int x = 0;
for (int j = 0, i = 0; j < n; j++) {
m[s[j]]++;
if (m[s[j]] == 1)
x++;
while (x > k && i <= j) {
m[s[i]]--;
if (m[s[i]] == 0)
x--;
i++;
}
ans = max(ans, j - i + 1);
}
return ans;
}
int lengthOfLongestSubstringTwoDistinct(string s){
return lengthOfLongestSubstringKDistinct(s, 2);
}
};
main(){
Solution ob;
cout << (ob.lengthOfLongestSubstringTwoDistinct("eceba"));
}Input
"eceba"
Output
3
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