Type of Triangle - Practice Coding Problems

Type of Triangle - Problem

Imagine you're a geometry teacher checking triangle homework! 📐

You are given a 3-element integer array nums representing the three sides of a potential triangle. Your task is to determine what type of triangle these sides can form, or if they can't form a triangle at all.

Triangle Types:

Equilateral: All three sides are equal (e.g., [5, 5, 5])
Isosceles: Exactly two sides are equal (e.g., [5, 5, 3])
Scalene: All three sides are different (e.g., [3, 4, 5])
None: The sides cannot form a valid triangle

Remember: For three sides to form a valid triangle, the sum of any two sides must be greater than the third side (Triangle Inequality Theorem).

Input & Output

example_1.py — Isosceles Triangle

$ Input: [3, 4, 5]

› Output: "scalene"

💡 Note: All three sides (3, 4, 5) are different lengths, and they satisfy the triangle inequality (3+4>5, 3+5>4, 4+5>3), so it forms a scalene triangle.

example_2.py — Equilateral Triangle

$ Input: [3, 3, 3]

› Output: "equilateral"

💡 Note: All three sides are equal (3 = 3 = 3), and they satisfy the triangle inequality, so it forms an equilateral triangle.

example_3.py — Invalid Triangle

$ Input: [1, 1, 3]

› Output: "none"

💡 Note: These sides cannot form a valid triangle because 1 + 1 = 2, which is not greater than 3. The triangle inequality is violated.

Constraints

nums.length == 3
1 ≤ nums[i] ≤ 10⁹
All sides are positive integers

Visualization

Tap to expand

Equilateral: All 3 sides equalExample: [5, 5, 5]IIsosceles: Exactly 2 sides equalExample: [5, 5, 3]SScalene: All sides differentExample: [3, 4, 5]✗None: Triangle inequality violated

Understanding the Visualization

Gather the Sticks

You have three sticks with lengths from the input array

Triangle Test

Check if any two sticks together are longer than the third stick

Count Matches

See how many sticks have the same length

Classify Result

Determine triangle type based on equal side count

Key Takeaway

🎯 Key Insight: Sort the sides first to optimize triangle inequality checking - you only need to verify that the sum of the two smaller sides exceeds the largest side!

Asked in

G Google 25 a Amazon 18 f Meta 15 ⊞ Microsoft 12

The optimal approach involves first checking the triangle inequality theorem (sum of any two sides must be greater than the third), then counting equal sides. The key insight is that after sorting, you only need to verify that the sum of the two shorter sides exceeds the longest side. Time complexity: O(1), Space complexity: O(1).

Common Approaches

Approach	Time	Space	Notes
✓ Direct Comparison Approach	O(1)	O(1)	Check all triangle inequalities directly, then count equal sides
Sorting + Optimization	O(1)	O(1)	Sort sides first, then check only one triangle inequality condition

Direct Comparison Approach — Algorithm Steps

Check if a + b > c, a + c > b, and b + c > a
If any condition fails, return 'none'
Count how many pairs of sides are equal
Return triangle type based on equal side count

Visualization

Tap to expand

Step-by-Step Walkthrough

Check First Inequality

Verify a + b > c

Check Second Inequality

Verify a + c > b

Check Third Inequality

Verify b + c > a

Count Equal Sides

Compare all pairs of sides

Code -

solution.c — C

#include <stdio.h>
#include <string.h>

char* solution(int* nums) {
    static char result[20];
    int a = nums[0], b = nums[1], c = nums[2];
    
    // Check triangle inequality
    if (a + b <= c || a + c <= b || b + c <= a) {
        strcpy(result, "none");
        return result;
    }
    
    // Count equal sides
    if (a == b && b == c) {
        strcpy(result, "equilateral");
    } else if (a == b || b == c || a == c) {
        strcpy(result, "isosceles");
    } else {
        strcpy(result, "scalene");
    }
    
    return result;
}

int main() {
    int nums[3];
    scanf("[%d,%d,%d]", &nums[0], &nums[1], &nums[2]);
    printf("%s\n", solution(nums));
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(1)

Fixed number of comparisons regardless of input

✓ Linear Growth

Space Complexity

O(1)

Only using a few variables for comparisons

✓ Linear Space

28.4K Views

Medium Frequency

~8 min Avg. Time

892 Likes

Ln 1, Col 1

Smart Actions

💡 Explanation

AI Ready

💡 Suggestion Tab to accept Esc to dismiss

// Output will appear here after running code

Code Editor Closed

Click the red button to reopen

Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Direct Comparison Approach — Algorithm Steps

Visualization

Code -

Time & Space Complexity

Select Compiler