Closest Number in Sorted Array(Ladder)

Description

Given a target number and an integer array A sorted in ascending order, find the index i in A such that A[i] is closest to the given target. Return -1 if there is no element in the array.

Notice:
There can be duplicate elements in the array, and we can return any of the indices with same value.

Example
Given [1, 2, 3] and target = 2, return 1.
Given [1, 4, 6] and target = 3, return 1.
Given [1, 4, 6] and target = 5, return 1 or 2.
Given [1, 3, 3, 4] and target = 2, return 0 or 1 or 2.

Challenge:
Time complexity in O(logn)

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 closestNumber(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]) {
                end = mid;
            } else {
                start = mid;
            }
        }
        if (abs(nums[start] - target) > abs(nums[end] - target)) {
            return end;
        } else {
            return start;
        }
        return -1;
    }
   };
   

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