Learn and practice the Greedy Techniques and Dynamic Programming patterns to solve coding interview problems.

Educative-77 in JavaScript: Accelerate Your Coding Interview Prep

This module teaches you two of the most important problem-solving techniques in the optimization domain: Greedy Techniques and Dynamic Programming. Not all problems require an exhaustive search through the solution space. Rather, consistently choosing the locally optimal solution can be proven to yield the globally optimal solution. In such situations, Greedy Techniques result in simple, highly efficient solutions. Other problems have a well-defined structure, where the same subproblem is encountered and solved multiple times. Dynamic Programming techniques allow us to compute once and reuse the solutions to recurring subproblems.

Optimization Techniques

# Statement

A big ship with numerous passengers is sinking, and there is a need to evacuate these people with the minimum number of life-saving boats. Each boat can carry, at most, two persons however, the weight of the people cannot exceed the carrying weight limit of the boat.

We are given an array, `people`, where `people[i]` is the weight of the $i^{th}$ person, and an infinite number of boats, where each boat can carry a maximum weight, `limit`. Each boat carries, at most, two people at the same time. This is provided that the sum of the weight of these people is under or equal to the weight limit.

You need to return the minimum number of boats to carry all persons in the array.

**Constraints:**

- $1 \leq$ `people.length` $\leq 5 \times 10^3$

- $1 \leq$ `people[i]` $\leq$ `limit` $\leq 3 \times 10^3$



How many boats are required to save everyone if we have the following inputs?

people = [3, 2, 2, 1, 1]

limit = 3

How many boats are required to save everyone if we have the following inputs?
people = [3, 2, 2, 1, 1]
limit = 3

How many boats are required to save everyone if we have the following inputs?

people = [3, 4, 5, 3, 4]

limit = 6

How many boats are required to save everyone if we have the following inputs?
people = [3, 4, 5, 3, 4]
limit = 6

Boats To Save People

Boats To Save People

// How to set up two pointers in an array

export default function twoPointers(array) {
 let left = 0,
 right = array.length - 1;

 while (left <= right) {
 left++;
 right--;
 }
}

# How to set up two pointers in an array

def two_pter(array):
 left = 0
 right = len(array) - 1
 while left <= right:
 left = left + 1
 right = right - 1

Help me debug only the function Boats to Save People . . 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 rescueBoats function and the other function(s) invoked in it/them. Do not review extra/helper files or functions not invoked in the solution function rescueBoats. 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 Greedy Techniques pattern used? Take your time and review the code.

Please provide a brief time complexity analysis of the function rescueBoats. While calculating time complexity, include the time complexity of built-in Javascript 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 rescueBoats. While calculating space complexity, include the space complexity of built-in Javascript 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

def evaluate_results(self) -> object:
 def rescue_boats(people, limit):
 
 people.sort()
 
 left = 0
 right = len(people) - 1

 boats = 0 

 while left <= right: 
 
 if people[left] + people[right] <= limit:
 left += 1 
 
 right -= 1

 boats += 1 
 return boats
 """
 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
 """
 # multiple outputs will be added at each index respectively for a single test_case
 expected_outputs = []
 input1 = self.__inputs[0]
 input2 = self.__inputs[1]
 expected = rescue_boats(input1, input2)
 # store the 1st expected output that should be displayed to the user 
 expected_outputs.append(expected)
 actual = self.__actual_outputs[0]
 if json.dumps(expected) == json.dumps(actual):
 self.__edu_result.store_result(expected_outputs, TestCaseResult.PASS)
 else:
 self.__edu_result.store_result(expected_outputs, TestCaseResult.FAIL)

 return self.__edu_result

export function rescueBoats(people, limit){
    
    // Replace the placeholder return statement below with your code
    
    return -1
}

boats_to_save_people.yaml

testcases:
  - name: "testcase 1"
    inputs:
    - 1 : [3, 1, 4, 2, 4]
    - 2 : 4
    output: 
    - 1 : 4
  - name: "testcase 2"
    inputs:
    - 1: [1, 1, 1, 1, 2]
    - 2: 3
    output:
    - 1 : 3
  - name: "testcase 3"
    inputs:
    - 1: [1, 2]
    - 2: 3
    output:
    - 1: 1
  - name: "testcase 4"
    inputs:
    - 1: [5, 5, 5, 5]
    - 2: 5
    output:
    - 1: 4
  - name: "testcase 5"
    inputs:
    - 1: [3, 2, 5, 5]
    - 2: 5
    output:
    - 1: 3


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 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)

 people = self.__inputs[0]
 limit = self.__inputs[1]
 # inputs can be accessed using self.__inputs starting from 0 to len(self.__inputs) - 1
 if not is_valid_1d_array(people):
 self.store_result(("Not a Valid 1D Integer Array."), ValidationFunction.FAIL)
 elif not (1 <= len(people) <= 5000):
 self.store_result ("expected 'people' to have 1 <= people.length <= 5000", ValidationFunction.FAIL)
 elif not all(1 <= num <= 3000 for num in people):
 self.store_result("'people' must consist of values from 1 to 3000 only", ValidationFunction.FAIL)
 elif not(1 <= limit <= 3000):
 self.store_result("'limit' must consist of values from 1 to 3000", ValidationFunction.FAIL)
 elif not all(num <= limit for num in people):
 self.store_result("'people[i]' must be less than or equal to 'limit'", ValidationFunction.FAIL)
 else:
 self.store_result("", ValidationFunction.PASS)

Try to solve the Boats to Save People challenge.

Greedy Techniques

Dynamic Programming

Conclusion

Boats to Save People

Statement

Examples

Understand the problem

Figure it out

Try it yourself