Binary Search Problem


Description

LeetCode Problem 704.

Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1.

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

Example 1:

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Input: nums = [-1,0,3,5,9,12], target = 9
Output: 4
Explanation: 9 exists in nums and its index is 4

Example 2:

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Input: nums = [-1,0,3,5,9,12], target = 2
Output: -1
Explanation: 2 does not exist in nums so return -1

Constraints:

  • 1 <= nums.length <= 10^4
  • -10^4 < nums[i], target < 10^4
  • All the integers in nums are unique.
  • nums is sorted in ascending order.


Sample C++ Code

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class Solution {
public:
    int search(vector<int>& nums, int target) {
        int n = nums.size()-1;
        int low = 0, high = n;
        while (low <= high) {
            int mid = low + (high-low) / 2;
            if (nums[mid] == target) 
                return mid;
            else if (nums[mid] > target) 
                high = mid -1;
            else 
                low = mid + 1;
        }
        return -1;
    }
};




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