canBalance challenge

But, they want us to split the array into two pieces
front and back

break at what index or point? just randomly we can break?

break at what index or point? just randomly we can break?

They want us to split the array into two parts that balance.
[1, 1, 1, 2, 1] can balance  1+1+1 == 2 +1
[2, 2,1,5] can balance 2+2+1 == 5  
We are search for the condition  that front == back
So, we have to search for the balance point.  
for( each split point in array){
      for( each element from first to split ){ add them up}
      for( each element from split to last){add them up}
      if front equals back return true
 }

canBalance([2, 3, 4, 1, 2]) → false

psedo code of logic approach is

1. loop through array from start
2. find the sum of left hand side
3. loop from backwards similar way
4. find the sum from right hand side
5. if both above sums equal return true
6. else return false.

below failing few tests . please advise

public boolean canBalance(int[] nums) {
		  for (int i = 0; i < nums.length; i++) {
			  int leftTotal=0;
			  leftTotal=leftTotal+nums[i];
			  for (int j = nums.length-1; j >i; j--) {
				  int rightTotal=0;
				  rightTotal=rightTotal+nums[i];
				  if(rightTotal==leftTotal){
					  return true;
				  }
				
			}
			
		}
		  
		  return false;
		}

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Expected      Run            
canBalance([1, 1, 1, 2, 1]) → true      true      OK      
canBalance([2, 1, 1, 2, 1]) → false      true      X      
canBalance([10, 10]) → true      true      OK      
canBalance([10, 0, 1, -1, 10]) → true      true      OK      
canBalance([1, 1, 1, 1, 4]) → true      true      OK      
canBalance([2, 1, 1, 1, 4]) → false      true      X      
canBalance([2, 3, 4, 1, 2]) → false      true      X      
canBalance([1, 2, 3, 1, 0, 2, 3]) → true      true      OK      
canBalance([1, 2, 3, 1, 0, 1, 3]) → false      true      X      
canBalance([1]) → false      false      OK      
canBalance([1, 1, 1, 2, 1]) → true      true      OK      
other tests
X

public class CanBalance {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int[] ar={1,1,1,2,1};
		System.out.println("canBalance value is--->"+canBalance(ar));

	}
	
	public static boolean canBalance(int[] nums) {
		  for (int i = 0; i < nums.length; i++) {
			  int leftTotal=0;
			  leftTotal=leftTotal+nums[i];
			  for (int j = nums.length-1; j >i; j--) {
				  int rightTotal=0;
				  rightTotal=rightTotal+nums[i];
				  if(leftTotal==rightTotal){
					  return true;
				  }
				
			}
			
		}
		  
		  return false;
		}


}

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canBalance value is--->true

When things aren't working as I planned, I add debug statements. That way I can see what is going on during the execution of my code.  For example,  

public class CanBalance {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int[] ar={1,1,1,2,1};
		System.out.println("canBalance value is--->"+canBalance(ar));

	}
	
	public static boolean canBalance(int[] nums) {
		  for (int i = 0; i < nums.length; i++) {
			  int leftTotal=0;
			  leftTotal=leftTotal+nums[i];
			  System.out.println("i is " + i + " leftTotal is " + leftTotal);
			  for (int j = nums.length-1; j >i; j--) {
				  int rightTotal=0;
				  rightTotal=rightTotal+nums[i];
				  System.out.println("j is " + j + " rightTotal is " + leftTotal);
				  if(leftTotal==rightTotal){
					  return true;
				  }
				
			}
			
		}  
		  return false;
		}
}

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The output is
i is 0 leftTotal is 1
j is 4 rightTotal is 1
canBalance value is--->true  

Now we see what the machine is doing. It is just comparing the first element with the first element. Which is true for this particular input.
Now let's change input to {1, 2, 3, 1, 0, 1, 3}
The output now is
i is 0 leftTotal is 1
j is 6 rightTotal is 1
canBalance value is--->true    

With the debug statements I have added, the code should print the totals in every iteration. Your code just  stops after a single iteration.  Another thing we can see from the second test, this statement

rightTotal=rightTotal+nums[i];

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is wrong. rightTotal should have equal to 3(at that point).  You have i where you should have j.

No your issue is when you reset the totals to 0.
You are resetting the total to 0 each time through the loop.
The loops should calculate the total from that direction so the reset should be ????

mlmcc

public boolean canBalance(int[] nums) {
		  int leftTotal=0;
		  int rightTotal=0;
		  for (int i = 0; i < nums.length; i++) {
			
			  leftTotal=leftTotal+nums[i];
			 // System.out.println("i is " + i + " leftTotal is " + leftTotal);
			  for (int j = nums.length-1; j >i; j--) {
				 
				  rightTotal=rightTotal+nums[j];
				//  System.out.println("j is " + j + " rightTotal is " + rightTotal);
				  if(leftTotal==rightTotal){
					  return true;
				  }
				
			}
			
		}
		  
		  return false;
		}

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passed couple of more tests

Expected      Run            
canBalance([1, 1, 1, 2, 1]) → true      true      OK      
canBalance([2, 1, 1, 2, 1]) → false      false      OK      
canBalance([10, 10]) → true      true      OK      
canBalance([10, 0, 1, -1, 10]) → true      true      OK      
canBalance([1, 1, 1, 1, 4]) → true      false      X      
canBalance([2, 1, 1, 1, 4]) → false      false      OK      
canBalance([2, 3, 4, 1, 2]) → false      true      X      
canBalance([1, 2, 3, 1, 0, 2, 3]) → true      false      X      
canBalance([1, 2, 3, 1, 0, 1, 3]) → false      false      OK      
canBalance([1]) → false      false      OK      
canBalance([1, 1, 1, 2, 1]) → true      true      OK      
other tests
OK      

public class CanBalance {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		//int[] ar={1,1,1,2,1};
		//System.out.println("canBalance value is--->"+canBalance(ar));
		
		//2, 1, 1, 2, 1
		int[] ar1={1, 2, 3, 1, 0, 1, 3};
		System.out.println("canBalance value is--->"+canBalance(ar1));

	}
	
	public static boolean canBalance(int[] nums) {
		  int leftTotal=0;
		  int rightTotal=0;
		  for (int i = 0; i < nums.length; i++) {
			
			  leftTotal=leftTotal+nums[i];
			  System.out.println("i is " + i + " leftTotal is " + leftTotal);
			  for (int j = nums.length-1; j >i; j--) {
				 
				  rightTotal=rightTotal+nums[j];
				  System.out.println("j is " + j + " rightTotal is " + rightTotal);
				  if(leftTotal==rightTotal){
					  return true;
				  }
				
			}
			
		}
		  
		  return false;
		}


}

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i is 0 leftTotal is 1
j is 6 rightTotal is 3
j is 5 rightTotal is 4
j is 4 rightTotal is 4
j is 3 rightTotal is 5
j is 2 rightTotal is 8
j is 1 rightTotal is 10
i is 1 leftTotal is 3
j is 6 rightTotal is 13
j is 5 rightTotal is 14
j is 4 rightTotal is 14
j is 3 rightTotal is 15
j is 2 rightTotal is 18
i is 2 leftTotal is 6
j is 6 rightTotal is 21
j is 5 rightTotal is 22
j is 4 rightTotal is 22
j is 3 rightTotal is 23
i is 3 leftTotal is 7
j is 6 rightTotal is 26
j is 5 rightTotal is 27
j is 4 rightTotal is 27
i is 4 leftTotal is 7
j is 6 rightTotal is 30
j is 5 rightTotal is 31
i is 5 leftTotal is 8
j is 6 rightTotal is 34
i is 6 leftTotal is 11
canBalance value is--->false



Trying to fox them too

Thank you, for inserting debug statements. Now you can see that  you need to fix the reset problem as pointed out by mlmcc

i like debug statement with with both i and totals which gives clear picture.


i is 0 leftTotal is 1
j is 4 rightTotal is 4
j is 3 rightTotal is 5
j is 2 rightTotal is 6
j is 1 rightTotal is 7
i is 1 leftTotal is 2
j is 4 rightTotal is 11


issue now is when i=i then jstarts from 4 again and the total needs to reset to 0 and start total with 5 then 5 for j=3 etc...which is not happening now?

I can see a difference between my code and yours. In my code I have one for loop to add left and another for loop to add right. Those two for loops are nested in another for loop.

can we do with 2 for loops instead of 3?

Please look at my pseudo code in my first comment.

can we do with 2 for loops instead of 3?

I don't know. Maybe some expert will show us how.

My solution has nested for loops . Something like  
for( whole array){
     for( front){ add them}
     for( back){add them}
     if front equals back return true
}

i see it. i am still thinking iif there is a way to fix with 2 loops if yes 3 loops unnecessary right?

int leftTotal=0;
              int rightTotal=0;

do i need to define above two on top of outer for loop ( for (int i = 0; i < nums.length; i++) {      )or one on top of outer for loop and another one(int rightTotal=0;) on top of inner for loop(  for (int j = nums.length-1; j >i; j--) {)

3 loops unnecessary right?

I don't know.

public boolean canBalance(int[] nums) {
		  int leftTotal=0;		 
		
		  for (int i = 0; i < nums.length; i++) {			
			  leftTotal=leftTotal+nums[i];
			 // System.out.println("i is " + i + " leftTotal is " + leftTotal);
			    int rightTotal=0;
			  for (int j = nums.length-1; j >i; j--) {				 
				  rightTotal=rightTotal+nums[j];
				  //System.out.println("j is " + j + " rightTotal is " + rightTotal);
			  }
				  if(leftTotal==rightTotal){
					  return true;
				  }				
			}			
				  
		  return false;
		}

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above passed all tests. I have to take out the if loop from inner for loop and also place rightTotal above inner for loop as below

int rightTotal=0;
                    for (int j = nums.length-1; j >i; j--) {

do i need to define ....

 I don't know. I can't really understand your code(thinking).   My thoughts :
in each iteration of outer for loop
add left
add right
if equal then break out
else reset

public class CanBalance {
	public static void main(String[] args) {
	
		int[] ar1={2, 1, 1, 2, 1};
		System.out.println("canBalance value is--->"+canBalance(ar1));
	}	
	public static boolean canBalance(int[] nums) {
		  int leftTotal=0;		 
		  
		  for (int i = 0; i < nums.length; i++) {			
			  leftTotal=leftTotal+nums[i];
			  System.out.println("i is " + i + " leftTotal is " + leftTotal);
			  int rightTotal=0;
			  for (int j = nums.length-1; j >i; j--) {				 
				  rightTotal=rightTotal+nums[j];
				  System.out.println("j is " + j + " rightTotal is " + rightTotal);
			  }
				  if(leftTotal==rightTotal){
					  return true;
				  }				
			}			
				  
		  return false;
		}
}

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i is 0 leftTotal is 2
j is 4 rightTotal is 1
j is 3 rightTotal is 3
j is 2 rightTotal is 4
j is 1 rightTotal is 5
i is 1 leftTotal is 3
j is 4 rightTotal is 1
j is 3 rightTotal is 3
j is 2 rightTotal is 4
i is 2 leftTotal is 4
j is 4 rightTotal is 1
j is 3 rightTotal is 3
i is 3 leftTotal is 6
j is 4 rightTotal is 1
i is 4 leftTotal is 7
canBalance value is--->false

any improvements, modifications, refinement to above code? how does your code looks like?

in each iteration of outer for loop
add left
start iteration of inner for loop
add right
if equal then return true
else return false

YOu need to test for equality after each time you add the right value.

mlmcc

YOu need to test for equality after each time you add the right value.

is that is reason why

 I have to take out the if loop from inner for loop and also place rightTotal above inner for loop(not above outer for loop) as below??

int rightTotal=0;                     for (int j = nums.length-1; j >i; j--) {

above passed all tests

Great! I am glad that you stayed with your own  idea.

Your code is better than mine. We learn from each other.

public class CanBalance {
	public static void main(String[] args) {
		int[] ar={4, 2, 3, 3};
		System.out.println("canBalance value is--->"+canBalance(ar));
	}
    public static boolean canBalance(int[] nums) {
		boolean result = false;
        int front = 0;
        int back = 0;
		for(int i = 0; i < nums.length; i++){
			for(int f = 0; f < i + 1 ; f++){
				front += nums[f];
				System.out.println("f is " + f + " front is " + front);
			}
			for(int b = i + 1; b < nums.length ; b++){
				back += nums[b];
				System.out.println("b is " + b + " back is " + back);
			}
			if(front == back){
				result = true;
				break;
			}
			else{
				front = 0;
				back = 0;
			}
		}
		return result;
    }
}

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 Output was  
f is 0 front is 4
b is 1 back is 2
b is 2 back is 5
b is 3 back is 8
f is 0 front is 4
f is 1 front is 6
b is 2 back is 3
b is 3 back is 6
canBalance value is--->true  

I stubbornly held to my first thoughts. I wastefully added the front(left) over and over. Your way is better.

iteration of outer for loop
     add left
     start iteration of inner for loop
            add right
            if equal then return true
     Loop inner
Loop outer
return false

mlmcc

iteration of outer for loop
     add left
     start iteration of inner for loop
            add right
            if equal then return true
     Loop inner
Loop outer
return false

how looping is different from iteration? i am thinking both same?

Same.  Just different terms.  Loop inner means return to start of iteration (loop) for next.

Only difference with your code is where you test for equality

mlmcc

Only difference with your code is where you test for equality

how your code looks like? did you use if loop inside inner for loo?

public boolean canBalance(int[] nums) {
		  int leftTotal=0;	
		   int rightTotal=0;
		
		  for (int i = 0; i < nums.length; i++) {			
			  leftTotal=leftTotal+nums[i];
			 // System.out.println("i is " + i + " leftTotal is " + leftTotal);
			 //   int rightTotal=0;
			  for (int j = nums.length-1; j >i; j--) {				 
				  rightTotal=rightTotal+nums[j];
				  //System.out.println("j is " + j + " rightTotal is " + rightTotal);
			  }
				  if(leftTotal==rightTotal){
					  return true;
				  }				
			}			
				  
		  return false;
		}

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Expected      Run            
canBalance([1, 1, 1, 2, 1]) → true      false      X      
canBalance([2, 1, 1, 2, 1]) → false      false      OK      
canBalance([10, 10]) → true      true      OK      
canBalance([10, 0, 1, -1, 10]) → true      true      OK      
canBalance([1, 1, 1, 1, 4]) → true      false      X      
canBalance([2, 1, 1, 1, 4]) → false      false      OK      
canBalance([2, 3, 4, 1, 2]) → false      false      OK      
canBalance([1, 2, 3, 1, 0, 2, 3]) → true      false      X      
canBalance([1, 2, 3, 1, 0, 1, 3]) → false      false      OK      
canBalance([1]) → false      false      OK      
canBalance([1, 1, 1, 2, 1]) → true      false      X      
other tests
OK      

why above code fails some tests if i move rightSum initialization line to the top of outer for loop rather than inner for loop??

int rightTotal=0;
		
		  for (int i = 0; i < nums.length; i++) {

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why above code fails some tests if i move rightSum initialization line to the top of outer for loop rather than inner for loop??

because you are not resetting the total value.

i is 0 leftTotal is 2
j is 4 rightTotal is 1
j is 3 rightTotal is 3
j is 2 rightTotal is 4
j is 1 rightTotal is 5
i is 1 leftTotal is 3
j is 4 rightTotal is 1
j is 3 rightTotal is 3
j is 2 rightTotal is 4
i is 2 leftTotal is 4
j is 4 rightTotal is 1
j is 3 rightTotal is 3
i is 3 leftTotal is 6
j is 4 rightTotal is 1
i is 4 leftTotal is 7
canBalance value is--->false

I see difference. As given below right Sum never resetted back to 0 if it is above outer loop. where as resetted perfectly if above inner for  loop producing correct output as above



i is 0 leftTotal is 2
j is 4 rightTotal is 1
j is 3 rightTotal is 3
j is 2 rightTotal is 4
j is 1 rightTotal is 5
i is 1 leftTotal is 3
j is 4 rightTotal is 6
j is 3 rightTotal is 8
j is 2 rightTotal is 9
i is 2 leftTotal is 4
j is 4 rightTotal is 10
j is 3 rightTotal is 12
i is 3 leftTotal is 6
j is 4 rightTotal is 13
i is 4 leftTotal is 7
canBalance value is--->false

why above code fails some tests if i move rightSum initialization line to the top of outer for loop rather than inner for loop??
because you are not resetting the total value.

now it is clear.

If given array is {1,1,1,1,4}

i   legtTotal  j    rightTotal(// i wonder how to draw a table in EE?)
0   1              4   4
                      3   5
                      2   6
                      1   7

1   2               4   4//here we need 4 value (which comes if i initialize rightTotal on top of inner for loop as it resetted when j inner loop start over triggered by increment of i from 0 to 1 etc...not 11 which comes if initializeat top of outer for loop as it keep on adding total till outer i loop completes.

Also if (leftTotal == rightTotal) check still inside outer for loop even though it is outside inner for loop which is whagt we wanted(to check each value of i we are finding all rightTotal values comparing with leftTotals.

i am closing this now