3024. Type of Triangle

Intuition

To determine the type of triangle, we need to:

1. Check if the three sides can form a valid triangle
2. Count the number of equal sides to determine the triangle type
3. Return the appropriate triangle type based on the conditions

Approach

1. First define constant strings for different triangle types:

   • equilateral: all sides equal
   • isosceles: two sides equal
   • scalene: no sides equal
   • none: not a valid triangle

2. Create a helper function checkTriangle to verify if three sides can form a valid triangle using the triangle inequality theorem:

   • sum of any two sides must be greater than the third side
   • check all three combinations: a+b>c, b+c>a, c+a>b

3. Use a map to count the frequency of each side length:

   • If any number appears 3 times, it's an equilateral triangle
   • If any number appears 2 times, it's potentially an isosceles triangle
   • Otherwise, it's potentially a scalene triangle

4. For isosceles and scalene cases, verify if they can form a valid triangle using checkTriangle

Complexity

• Time complexity: O(1)
• Space complexity: O(1)

Keywords

• Triangle Inequality Theorem
• Hash Map

Code

func triangleType(nums []int) string {
    var (
        equ string = "equilateral"
        iso string = "isosceles"
        sca string = "scalene"
        non string = "none"
    )

    checkTriangle := func() bool {
        a, b, c := nums[0], nums[1], nums[2]
        if (a + b > c) && (b + c > a) && (c + a > b) {
            return true
        }
        return false
    }

    record := make(map[int]int)
    for _, num := range nums {
        record[num] += 1
        if record[num] == 3 {
            return equ
        }
    }

    for _, v := range record {
        if v == 2 {
            if checkTriangle() {
                return iso
            }
            return non
        }
    }

    if checkTriangle() {
        return sca
    }

    return non
}