704_binary_search.md

704 - Binary Search

leetcode link

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:

1. You may assume that all elements in nums are unique.
2. n will be in the range [1, 10000].
3. The value of each element in nums will be in the range [-9999, 9999].

Iterative solution

// 18/09/2020
// iterative solution
int search(vector<int>& nums, int target) {
    int l = 0, r = nums.size();
    while(l<r){
        int mid = l+(r-l)/2;
        if(nums[mid]<target)
            l = mid +1;
        else if(nums[mid]>target)
            r = mid;
        else
            return mid;
    }
    return -1;
}

Recursive solution

// 18/09/2020
// recursive solution
int search(vector<int>& nums, int target) {
    return search(nums, target, 0, nums.size());
}

int search(vector<int>& nums, int target, int l, int r){
    if (l>=r) 
        return -1;
    int mid = l+(r-l)/2;
    if (nums[mid]<target)
        return search(nums, target, mid +1, r);
    else if (nums[mid]>target)
        return search(nums, target, l, mid);
    else
        return mid;
}

TODO : solutions with iterators