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Three Equal Parts in C++
Suppose we have one array A of 0s and 1s, we have to divide the array into 3 non-empty parts such that all of these parts represent the same binary value. If that is possible, return any [i, j] with i+1 < j, such that −
A[0], A[1], ..., A[i] is the first part;
A[i+1], A[i+2], ..., A[j-1] is the second part, and
A[j], A[j+1], ..., A[A.length - 1] is the third part.
All three parts have equal binary value. If that is not possible, return [-1, -1].
So, if the input is like [0,1,0,1,1], then the output will be [0,4]
To solve this, we will follow these steps −
Define a function getIdx(), this will take an array a, left, right,
while (left < right and a[left] is same as 0), do −
(increase left by 1)
while right < (int)a.size(), do −
if a[left] is not equal to a[right], then, return -1
(increase left by 1), (increase right by 1)
return left - 1
From the main method do the following −
Define an array ret of size 2 fill this with -1
num := 0, n := size of A
for initialize i := 0, when i < n, update (increase i by 1), do −
num := num + 1 when (A[i] is same as 1), otherwise 0
if num mod 3 is not equal to 0, then −
return ret
if num is same as 0, then −
return { 0, 2 }
req := num / 3
idx := n - 1
for initialize temp := 0, when idx >= 0 and temp < req, update (decrease idx by 1), do
temp := temp + 1 when (A[idx] is same as 1), otherwise 0
(increase idx by 1)
firstEnd := getIdx(A, 0, idx)
if firstEnd < 0, then −
return ret
secondEnd := getIdx(A, firstEnd + 1, idx)
if secondEnd < 0, then −
return ret
return { firstEnd, secondEnd + 1 }
Let us see the following implementation to get better understanding −
Example
#include <bits/stdc++.h>
using namespace std;
void print_vector(vector<auto> v){
cout << "[";
for(int i = 0; i<v.size(); i++){
cout << v[i] << ", ";
}
cout << "]"<<endl;
}
class Solution {
public:
vector<int> threeEqualParts(vector<int>& A){
vector<int> ret(2, -1);
int num = 0;
int n = A.size();
for (int i = 0; i < n; i++) {
num += (A[i] == 1);
}
if (num % 3 != 0)
return ret;
if (num == 0) {
return { 0, 2 };
}
int req = num / 3;
int idx = n - 1;
for (int temp = 0; idx >= 0 && temp < req; idx--) {
temp += A[idx] == 1;
}
idx++;
int firstEnd = getIdx(A, 0, idx);
if (firstEnd < 0)
return ret;
int secondEnd = getIdx(A, firstEnd + 1, idx);
if (secondEnd < 0)
return ret;
return { firstEnd, secondEnd + 1 };
}
int getIdx(vector<int>& a, int left, int right){
while (left < right && a[left] == 0)
left++;
while (right < (int)a.size()) {
if (a[left] != a[right])
return -1;
left++;
right++;
}
return left - 1;
}
};
main(){
Solution ob;
vector<int> v = {0,1,0,1,1};
print_vector(ob.threeEqualParts(v));
}Input
{0,1,0,1,1}Output
[1, 4, ]
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