704.binary-search.cpp

/*
 * @lc app=leetcode id=704 lang=cpp
 *
 * [704] Binary Search
 *
 * https://leetcode.com/problems/binary-search/description/
 *
 * algorithms
 * Easy (45.35%)
 * Total Accepted:    35.2K
 * Total Submissions: 77.5K
 * Testcase Example:  '[-1,0,3,5,9,12]\n9'
 *
 * Given a sorted (in ascending order) integer array nums of n elements and a
 * target value, write a function to search target in nums. If target exists,
 * then return its index, otherwise return -1.
 *
 *
 * Example 1:
 *
 *
 * Input: nums = [-1,0,3,5,9,12], target = 9
 * Output: 4
 * Explanation: 9 exists in nums and its index is 4
 *
 *
 *
 * Example 2:
 *
 *
 * Input: nums = [-1,0,3,5,9,12], target = 2
 * Output: -1
 * Explanation: 2 does not exist in nums so return -1
 *
 *
 *
 *
 * Note:
 *
 *
 * You may assume that all elements in nums are unique.
 * n will be in the range [1, 10000].
 * The value of each element in nums will be in the range [-9999, 9999].
 *
 *
 */
#include <vector>
using namespace std;

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