Learn and practice the Two Pointers, and Modified Binary Search patterns to solve coding interview problems.

Speedrun the Google Coding Interview: Top Problems in Java

This module groups together two of the most common patterns that may be used to solve problems where the input data is linear: Two Pointers and Modified Binary Search. Both the Two Pointers and the Modified Binary Search patterns derive their power from their ability to efficiently reduce the size of the search space, that is, both exemplify the divide and conquer approach to problem-solving. After completing this module, we will have the knowledge of how to use this set of related patterns to solve a diverse range of problems.

Two Pointers & Co.

# Statement
 
Given an array of integers, `nums`, and an integer value, `target`, determine if there are any three integers in `nums` whose sum is equal to the `target`, that is, `nums[i] + nums[j] + nums[k] == target`. Return TRUE if three such integers exist in the array. Otherwise, return FALSE.

> **Note:** A valid triplet consists of elements with _distinct_ indexes. This means, for the triplet `nums[i], nums[j]`, and `nums[k]`, `i` $\not =$ `j`, `i` $\not =$ `k` and `j` $\not =$ `k`.


**Constraints:**
* $3$ $\leq$ `nums.length` $\leq$ $500$
* $-10^3$ $\leq$ `nums[i]` $\leq$ $10^3$
* $-10^3$ $\leq$ `target` $\leq$ $10^3$


# Examples

# Understand the problem


Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:




What should be the output if the following set of inputs is provided?

nums = [2, 3, 1]

target = 6

What should be the output if the following set of inputs is provided?
nums = [2, 3, 1]
target = 6

What should be the output if the following set of inputs is provided?

nums = [1, -1, 1]

target = 2

What should be the output if the following set of inputs is provided?
nums = [1, -1, 1]
target = 2

What should be the output if the following set of inputs is provided?

nums = [1, 2, 4, 6, 8, 20]

target = 31

What should be the output if the following set of inputs is provided?
nums = [1, 2, 4, 6, 8, 20]
target = 31

You are given the following inputs:

nums = [1, 2, 4, 6, 8, 20]

target = 31

If you could make _one_ replacement in the given array to get to the target, which replacement would you make?

Select all that apply.

You are given the following inputs:
nums = [1, 2, 4, 6, 8, 20]
target = 31
If you could make one replacement in the given array to get to the target, which replacement would you make?
Select all that apply.

Sum of Three Values

Sum of Three Values

# Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.


Implement your solution in `SumOfThree.java` in the following coding playground. The supporting code template provided in `TwoPointers.java` is meant to assist in developing your solution to the problem.



import java.util.*;

public class SumOfThree{
   public static boolean findSumOfThree(int[] nums, int target) {
      
      // Replace this placeholder return statement with your code
      return false;
   }
}

// Template for how to set up two pointers in an array
import java.util.*;
class TwoPointers{
 static void twoPointers(int[] array){
 int left = 0;
 int right = array.length - 1;
 while (left <= right){
 left = left + 1;
 right = right -1;
 }
 }
}

Help me debug only the function Sum of Three Values . . I don't need the corrected code.I don't want explanations or code review. Just provide me the exact and to-the-point error that helps me run the code successfully on the test cases provided.

Please help me understand why this code failed for the last failed test case. Don't give me the corrected code. . If yes, then Just provide me the exact and to-the-point error that helps me run the code successfully on the test cases provided.

Your current task is to review only the findSumOfThree function and the other function(s) invoked in it/them. Do not review extra/helper files or functions not invoked in the solution function findSumOfThree. Do not review the code of data structures objects instantiated like a binary tree, linked list, trie, union find, etc., in the solution functions. Just review the solution/algorithm function of the problem. Also, Answer the following questions: Is the Two Pointers pattern used? Take your time and review the code.

Please provide a brief time complexity analysis of the function findSumOfThree. While calculating time complexity, include the time complexity of built-in Java functions invoked by the code. The Answer should be to the point and in a few lines.

Please provide a brief Space complexity analysis of the function findSumOfThree. While calculating space complexity, include the space complexity of built-in Java functions invoked by the code. Do not include the space used for the input parameters and the space used for just returning an output(not used as a scratch space). The Answer should be to the point and in a few lines

OneDArray

import ds_v1.DataStructure.DataStructure;
import java.util.*;
public class OneDArray extends DataStructure {
 int[] values = {};


 public OneDArray() {
 //values = {};
 }
 

 public OneDArray(int[] val){
 this.values = new int [val.length];
 for(int i =0; i < val.length;i++){
 values[i] = val[i];
 }
 
 }

 public String toString() {
 return Arrays.toString(values);
 }

 @Override
 public OneDArray construct(String new_value, Integer type_of_ds) {
 String new_value1 = new_value.substring(1,new_value.length() - 1);
 String[] string = new_value1.split(",");
 int[] arr = new int[string.length];
 
 for (int i = 0; i < string.length; i++) {
 arr[i] = Integer.valueOf(string[i]);
 }
 return new OneDArray(arr);

 }

 @Override
 public String traverse(Object input, Integer type_of_ds) {
 
 return input.toString();
 }

}

def evaluate_results(self) -> object:
 """
 self.__inputs is the list of inputs that are passed as input to function
 self.__actual_output is a list of outputs that is produced by the learner's code
 return : self.__edu__result object
 """
 def find_sum_of_three(nums, target):
 nums.sort()

 for i in range(0, len(nums)-2):
 low = i + 1
 high = len(nums) - 1

 while low < high:
 triplet = nums[i] + nums[low] + nums[high]

 if triplet == target:
 return True
 
 elif triplet < target:
 low += 1
 
 else:
 high -= 1
 
 return False
 



 # multiple outputs will be added at each index respectively for a single test_case
 expected_outputs = [] 
 expected = find_sum_of_three(self.__inputs[0],self.__inputs[1])
 actual = self.__actual_outputs[0]
 # store the 1st expected output that should be displayed to the user 
 expected_outputs.append(expected) 
 if expected == actual:
 self.__edu_result.store_result(expected_outputs, TestCaseResult.PASS)
 else:
 self.__edu_result.store_result(expected_outputs, TestCaseResult.FAIL)

 return self.__edu_result

public class Main{
 public static boolean findSumOfThree1(OneDArray c, int target) {
    boolean m = SumOfThree.findSumOfThree(c.values, target);
    return m;
      
 }
}

PrivateTestCases.yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : [1, -1, 0]
    - 2 : -1
    output: 
    - 1 : False
  - name: "testcase 2"
    inputs:
    - 1: [3, 7, 1, 2, 8, 4, 5]
    - 2: 10
    output:
    - 1: True
  - name: "testcase 3"
    inputs:
    - 1: [3, 7, 1, 2, 8, 4, 5]
    - 2: 21
    output:
    - 1: False
  - name: "testcase 4"
    inputs:
    - 1: [-1, 2, 1, -4, 5, -3]
    - 2: -8
    output:
    - 1: True
  - name: "testcase 5"
    inputs:
    - 1: [-1, 2, 1, -4, 5, -3]
    - 2: 0
    output:
    - 1: True

def sum(input_1, input_2):
    return input_1+input_2

def validate_inputs(self) -> None:
 """
 self.__inputs is the list of inputs that are passed as input to the function.
 Store the result using the self.store_result(error_msg, status).
 Return: void
 """

 def is_valid_1d_array(arr):
 if not isinstance(arr, list):
 return False # Not a valid 1D array if it's not a list
 
 return all(isinstance(elem, int) and not isinstance(elem, bool) for elem in arr)

 # Inputs can be accessed using self.__inputs starting from 0 to len(self.__inputs) - 1
 if not is_valid_1d_array(self.__inputs[0]):
 self.store_result(("Invalid test case."), ValidationFunction.FAIL)
 elif len(self.__inputs[0]) < 3 or len(self.__inputs[0]) > 500:
 self.store_result("Expected length of Input 1 to be between 3 and 500.", ValidationFunction.FAIL)
 elif any(x < -1000 or x > 1000 for x in self.__inputs[0]):
 self.store_result("Input 1 should be an integer between -1000 and 1000.", ValidationFunction.FAIL)
 elif self.__inputs[1] < -1000 or self.__inputs[1] > 1000:
 self.store_result("Input 2 should be an integer between -1000 and 1000.", ValidationFunction.FAIL)
 else:
 self.store_result("", ValidationFunction.PASS)

Two Pointers

Modified Binary Search

Conclusion

Sum of Three Values

Statement

Examples

Understand the problem

Figure it out!

Try it yourself