LeetCode-in-Java

3909. Compare Sums of Bitonic Parts

Medium

You are given a bitonic array nums of length n.

Split the array into two parts:

• Ascending part: from index 0 to the peak element (inclusive).
• Descending part: from the peak element to index n - 1 (inclusive).

The peak element belongs to both parts.

Return:

• 0 if the sum of the ascending part is greater.
• 1 if the sum of the descending part is greater.
• -1 if both sums are equal.

Notes:

• A bitonic array is an array that is strictly increasing up to a single peak element and then strictly decreasing.
• An array is said to be strictly increasing if each element is strictly greater than its previous one (if exists).
• An array is said to be strictly decreasing if each element is strictly smaller than its previous one (if exists).

Example 1:

Input: nums = [1,3,2,1]

Output: 1

Explanation:

• Peak element is nums[1] = 3
• Ascending part = [1, 3], sum is 1 + 3 = 4
• Descending part = [3, 2, 1], sum is 3 + 2 + 1 = 6
• Since the descending part has a larger sum, return 1.

Example 2:

Input: nums = [2,4,5,2]

Output: 0

Explanation:

• Peak element is nums[2] = 5
• Ascending part = [2, 4, 5], sum is 2 + 4 + 5 = 11
• Descending part = [5, 2], sum is 5 + 2 = 7
• Since the ascending part has a larger sum, return 0.

Example 3:

Input: nums = [1,2,4,3]

Output: -1

Explanation:

• Peak element is nums[2] = 4
• Ascending part = [1, 2, 4], sum is 1 + 2 + 4 = 7
• Descending part = [4, 3], sum is 4 + 3 = 7
• Since both parts have equal sums, return -1.

Constraints:

• 3 <= n == nums.length <= 105
• 1 <= nums[i] <= 109
• nums is a bitonic array.

Solution

public class Solution {
    public int compareBitonicSums(int[] nums) {
        long asc = 0;
        long desc = 0;
        int i;
        for (i = 0; i < nums.length - 1; i++) {
            asc += nums[i];
            if (nums[i] > nums[i + 1]) {
                break;
            }
        }
        for (; i < nums.length; i++) {
            desc += nums[i];
        }
        if (asc == desc) {
            return -1;
        }
        return asc > desc ? 0 : 1;
    }
}

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