34. Find First and Last Position of Element in Sorted Array leetCode

 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]


C++:

class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        vector<int>result;
        int firstIndex= firstOcc(nums,target);
        int lastIndex = lastOcc(nums,target);
        result.push_back(firstIndex);
        result.push_back(lastIndex);
        return result;
       
    }
    int firstOcc(vector<int>& nums, int target){
        int start = 0;
        int end = nums.size()-1;
        int  mid=start+(end-start)/2;
        int ans = -1;
        while(start <= end){
           
            if(target==nums[mid]){
                ans = mid;
                end = mid-1;
            }
            else if(target >nums[mid]){
                start = mid+1;
            }
            else{
                end = mid-1;
            }
             mid=start+(end-start)/2;
        }
        return ans;
    }
    int lastOcc(vector<int>& nums, int target){
        int start = 0;
        int end = nums.size()-1;
        int ans = -1;
         int  mid=start+(end-start)/2;
        while(start <= end){
         
           
            if(target == nums[mid]){
                ans = mid;
                start = mid+1;
            }
            else if(target > nums[mid]){
                start = mid+1;
            }
            else{
                end = mid-1;
            }
           mid=start+(end-start)/2;
        }
        return ans;
       
    }
};





Java:

class Solution {
    public int[] searchRange(int[] nums, int target) {
        int[] index = new int[2];
 if (nums == null || nums.length == 0) {
            return new int[] {-1, -1};
        index[0] = firstOccurrence(nums, target);
        index[1] = lastOccurrence(nums, target);
        return index;
    }

    private int firstOccurrence(int[] nums, int target) {
        int start = 0;
        int end = nums.length - 1;
        int ans = -1;

        while (start <= end) {
            int mid = start + (end - start) / 2;

            if (nums[mid] == target) {
                ans = mid;
                end = mid - 1; // keep searching on the left
            } else if (nums[mid] < target) {
                start = mid + 1;
            } else {
                end = mid - 1;
            }
        }

        return ans;
    }

    private int lastOccurrence(int[] nums, int target) {
        int start = 0;
        int end = nums.length - 1;
        int ans = -1;

        while (start <= end) {
            int mid = start + (end - start) / 2;

            if (nums[mid] == target) {
                ans = mid;
                start = mid + 1; // keep searching on the right
            } else if (nums[mid] < target) {
                start = mid + 1;
            } else {
                end = mid - 1;
            }
        }

        return ans;
    }
}


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