704. Binary Search

Problem:

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].

思路：

Solution (C++):

int search(vector<int>& nums, int target) {
    int low = 0, high = nums.size()-1;
    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;
}

性能：

Runtime: 48 ms  Memory Usage: 8.8 MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB