problem

Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.

If target is not found in the array, return [-1, -1].

You must write an algorithm with O(log n) runtime complexity.

 

Example 1:

Input: nums = [5,7,7,8,8,10], target = 8
Output: [3,4]

Example 2:

Input: nums = [5,7,7,8,8,10], target = 6
Output: [-1,-1]

Example 3:

Input: nums = [], target = 0
Output: [-1,-1]

 

Constraints:

  • 0 <= nums.length <= 105
  • -109 <= nums[i] <= 109
  • nums is a non-decreasing array.
  • -109 <= target <= 109

submission

impl Solution {
    pub fn search_range(nums: Vec<i32>, target: i32) -> Vec<i32> {
        // a standard binary search with custom comparator
        fn helper(
            nums: &[i32],
            target: i32,
            f: impl Fn(i32, i32) -> bool,
        ) -> usize {
            let (mut left, mut right) = (0, nums.len());
            while left < right {
                let mid = left + (right - left) / 2;
                if f(nums[mid], target) {
                    left = mid + 1;
                } else {
                    right = mid;
                }
            }
            left
        }
        // lower bound and upper bound
        let lower = helper(&nums, target, |l, r| l < r) as i32;
        let upper = helper(&nums, target, |l, r| l <= r) as i32;
        match lower == upper {
            // this means nums doesn't contain target
            true => vec![-1, -1],
            false => vec![lower, upper - 1],
        }
    }
}