List Partitioning - Amazon Top Interview Questions
Problem Statement :
Given a list of strings strs, containing the strings "red", "green" and "blue", partition the list so that the red come before green, which come before blue.
This should be done in \mathcal{O}(n)O(n) time.
Bonus: Can you do it in \mathcal{O}(1)O(1) space? That is, can you do it by only rearranging the list (i.e. without creating any new strings)?
Constraints
n ≤ 100,000 where n is the length of strs.
Example 1
Input
strs = ["green", "blue", "red", "red"]
Output
["red", "red", "green", "blue"]
Solution :
Solution in C++ :
void swap(vector<string>& A, int i, int j) {
string t = A[i];
A[i] = A[j];
A[j] = t;
}
vector<string> solve(vector<string>& A) {
int j = 0;
for (int i = 0; i < A.size(); i++) {
if (A[i] == "red") {
swap(A, j, i);
j++;
}
}
for (int i = 0; i < A.size(); i++) {
if (A[i] == "green") {
swap(A, j, i);
j++;
}
}
return A;
}
Solution in Python :
class Solution:
def solve(self, s):
def partition(s, start, word):
for i in range(start, len(s)):
if s[i] == word:
s[i], s[start] = s[start], s[i]
start += 1
return start
start = partition(s, 0, "red")
partition(s, start, "green")
return s
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