Electricity Bill Calculator - Problem

Calculate the electricity bill for a given number of units consumed using a slab-based pricing system:

First 100 units: $1.0 per unit
Next 200 units (101-300): $1.5 per unit
Above 300 units: $2.0 per unit

Given the number of units consumed, return the total bill amount.

Note: The billing is cumulative - you pay different rates for different portions of your consumption.

Input & Output

Example 1 — Basic Case (Within Second Slab)

$ Input: units = 250

› Output: 325.0

💡 Note: First 100 units: 100 × $1.0 = $100. Next 150 units: 150 × $1.5 = $225. Total: $100 + $225 = $325

Example 2 — Small Consumption (First Slab Only)

$ Input: units = 75

› Output: 75.0

💡 Note: Only 75 units consumed, all in first slab: 75 × $1.0 = $75

Example 3 — High Consumption (All Three Slabs)

$ Input: units = 450

› Output: 725.0

💡 Note: First 100: $100, Next 200: $300, Remaining 150: 150 × $2.0 = $300. Total: $100 + $300 + $300 = $700

Constraints

1 ≤ units ≤ 10⁶
Return value should be a floating-point number

Visualization

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Asked in

A Accenture 15 T TCS 12

The key insight is to handle electricity billing as a slab-based system where different rates apply to different consumption ranges. The best approach uses conditional logic to calculate costs for each applicable slab. Time: O(1), Space: O(1)

Common Approaches

✓ Conditional Slabs

⏱️ Time: O(1) Space: O(1)

Check which slab the units fall into and calculate the bill by adding the cost of each slab up to the consumed units. Handle three cases: ≤100, 101-300, and >300 units.

Cumulative Calculation

⏱️ Time: O(1) Space: O(1)

Start with zero bill and add the cost of each slab sequentially until we've accounted for all units. More systematic approach that scales better if more slabs are added.

Conditional Slabs — Algorithm Steps

Check if units ≤ 100, return units × $1
Check if units ≤ 300, return (100 × $1) + ((units-100) × $1.5)
For units > 300, return (100 × $1) + (200 × $1.5) + ((units-300) × $2)

Visualization

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Step-by-Step Walkthrough

Check Range

Determine which slab the units fall into

Calculate Each Slab

Add cost for each applicable slab tier

Return Total

Sum up all slab costs for final bill

Code -

solution.c — C

#include <stdio.h>

double solution(int units) {
    if (units <= 100) {
        return units * 1.0;
    } else if (units <= 300) {
        return (100 * 1.0) + ((units - 100) * 1.5);
    } else {
        return (100 * 1.0) + (200 * 1.5) + ((units - 300) * 2.0);
    }
}

int main() {
    int units;
    scanf("%d", &units);
    double result = solution(units);
    printf("%f\n", result);
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(1)

Constant time as we only perform fixed number of arithmetic operations

✓ Linear Growth

Space Complexity

O(1)

Only using a few variables to store intermediate calculations

✓ Linear Space

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Electricity Bill Calculator - Problem

Input & Output

Constraints

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Related Problems

Common Approaches

Conditional Slabs — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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