Amazon

Paypal

2020-10-08

### Question:

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]`.

### Solution:

This will be a template for binary search

``````class Solution {
public int search(int[] nums, int target) {
if (nums == null || nums.length == 0) {
return -1;
}

int start = 0;
int end = nums.length - 1;

while (start + 1 < end) {
int mid = start + (end - start) / 2;
if (nums[mid] == target) {
return mid;
} else if (nums[mid] > target) {
end = mid;
} else {
start = mid;
}
}

if (nums[start] == target) {
return start;
}

if (nums[end] == target) {
return end;
}

return -1;

}
}
``````

Using `start + 1 < end` will avoid the infinite loop problem as following. If we are having `[1,1]`, it will cause infinite loop.

``````while (start <= end) {
mid = (start + end) / 2;
if (A[mid] <= target) {
start = mid;
} else {
end = mid - 1;
}
}
``````