L14 First Position of Target

For a given sorted array (ascending order) and atargetnumber, find the first index of this number inO(log n)time complexity.

If the target number does not exist in the array, return-1.

Example

If the array is[1, 2, 3, 3, 4, 5, 10], for given target3, return2.

Challenge

If the count of numbers is bigger than 2^32, can your code work properly?

因为找第一个位置，所以先判断start。

public int binarySearch(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) {
            start = mid;
        } else if (nums[mid] > target) {
            end = mid;
        } else {
            end = mid;
        }
    }

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

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

    return -1;