Classical Binary Search(Ladder)

Description

Find any position of a target number in a sorted array. Return -1 if target does not exist.

Example:
Given [1, 2, 2, 4, 5, 5].
For target = 2, return 1 or 2.
For target = 5, return 4 or 5.
For target = 6, return -1.

Challenge: O(logn) time

Link

Lintcode_ladder

Method

1. Binary Search
2. x

Example

1. 1

   class Solution {
   public:
    /**
     * @param A an integer array sorted in ascending order
     * @param target an integer
     * @return an integer
     */
    int findPosition(vector<int>& nums, int target) {
        // Write your code here
        if (nums.empty()) {
            return -1;
        }
        int start = 0;
        int end = nums.size()-1;
        while (start+1 < end) {
            int mid = start + (end-start)/2;
            if (target == nums[mid]) {
               return mid;
            } else if (target > nums[mid]) {
                start = mid;
            } else {
                end = mid;
            }
        }
        if (target == nums[start]) {
            return start;
        }
        if (target == nums[end]) {
            return end;
        }
        return -1;
    }
   };
   

Similar problems

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Tags

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