# 2774. Array Upper Bound

## Description

Write code that enhances all arrays such that you can call the upperBound() method on any array and it will return the last index of a given target number. nums is a sorted ascending array of numbers that may contain duplicates. If the target number is not found in the array, return -1.

Example 1:

Input: nums = [3,4,5], target = 5
Output: 2
Explanation: Last index of target value is 2


Example 2:

Input: nums = [1,4,5], target = 2
Output: -1
Explanation: Because there is no digit 2 in the array, return -1.

Example 3:

Input: nums = [3,4,6,6,6,6,7], target = 6
Output: 5
Explanation: Last index of target value is 5


Constraints:

• 1 <= nums.length <= 104
• -104 <= nums[i], target <= 104
• nums is sorted in ascending order.

Follow up: Can you write an algorithm with O(log n) runtime complexity?

## Solutions

• declare global {
interface Array<T> {
upperBound(target: number): number;
}
}

Array.prototype.upperBound = function (target: number) {
let left = 0;
let right = this.length;
while (left < right) {
const mid = (left + right) >> 1;
if (this[mid] > target) {
right = mid;
} else {
left = mid + 1;
}
}
return left > 0 && this[left - 1] == target ? left - 1 : -1;
};

// [3,4,5].upperBound(5); // 2
// [1,4,5].upperBound(2); // -1
// [3,4,6,6,6,6,7].upperBound(6) // 5