# Three Equal Parts in C++

C++Server Side ProgrammingProgramming

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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, A, ..., 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

Live Demo

#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, ]