【每日一算】二分查找

給定一個整形有序數組，如何找出某一整數是否在數組中，以及該整數在數組中對應的下標？

例如：

int[] arr = {1,4,6,11,23}
int target = 11
找出target在arr中對應位置的下標
結果是:index = 3

這是一個典型的二分查找問題，代碼以下：

public class Solution_1 {

    private static int findTargetIndex(int[] nums, int target) {
        int left = 0;
        int right = nums.length - 1;
        while (left <= right) {
           // int mid = (right+left)/2 可能引發溢出問題
                
            int mid = (right - left) / 2 + left;
            if (nums[mid] == target) {
                return mid;
            }
            if (nums[mid] > target) {
                right = mid - 1;
            } else {
                left = mid + 1;
            }

        }

        return -1;
    }

    public static void main(String[] args) {

        int[] arr = new int[10000000];
        for (int i = 0; i < 10000000; i++) {
            arr[i] = i;
        }
        int target = 111111;
        int targetIndex = findTargetIndex(arr, target);
        System.out.println("targetIndex = " + targetIndex);
    }
}