Search for a Range - Leetcode

searchRange.java

/*
Given a sorted array of integers, find the starting and ending position of a given target value.

Your algorithm's runtime complexity must be in the order of O(log n).

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

For example,
Given [5, 7, 7, 8, 8, 10] and target value 8,
return [3, 4].
*/
public class Solution {
    public int[] searchRange(int[] A, int target) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int[] ret = new int[2];
        ret[0] = search_left_most(A, target);
        ret[1] = search_right_most(A, target);
        return ret;
    }
    
    public int search_left_most(int[] A, int target) {
        int left = 0;
        int right = A.length - 1;
        while(right >= left) {
            int mid = (right + left) / 2;
            if(A[mid] == target) {
                if(mid == 0) return mid;
                if(A[mid-1] == target) right = mid - 1;
                else return mid;
            } else if(A[mid] > target) {
                right = mid - 1;
            } else if(A[mid] < target) {
                left = mid + 1;
            }
        }
        return -1;
    }
    
    public int search_right_most(int[] A, int target) {
        int left = 0;
        int right = A.length - 1;
        while(right >= left) {
            int mid = (right + left) / 2;
            if(A[mid] == target) {
                if(mid == A.length - 1) return mid;
                if(A[mid+1] == target) left = mid + 1;
                else return mid;
            } else if(A[mid] > target) {
                right = mid - 1;
            } else if(A[mid] < target) {
                left = mid + 1;
            }
        }
        return -1;
    }
}