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二分法查找高效率--Java

南陵王梁枫 2022-03-17 阅读 41
public class 二分法 {
    static int count;

    public static void main(String[] args) {
        // 在一个数组中查找一个数的下标:
        int[] arr = {1, 3, 4, 7, 9, 11};
        System.out.println(binarySearch(arr, 3));
        System.out.println(count);
    }

    public static int binarySearch(int[] arr, int target) {
        if (arr.length < 1) {
            throw new RuntimeException("数组有误");
        }
        if (target < arr[0] || target > arr[arr.length - 1]) {
            count++;
            return -1;
        }
        if (target == arr[0]) {
            count++;
            return 0;
        }
        if (target == arr[arr.length - 1]) {
            count++;
            return arr.length - 1;
        }
        int left = 0;
        int right = arr.length - 1;
        int mid;
        while (left + 1 < right) {
            mid = (left + right) / 2;
            if (target == arr[mid]) {
                return mid;
            } else if (target > arr[mid]) {
                left = mid;
            } else {
                right = mid;
            }
            if (target == arr[left]) {
                return left;
            }
            if (target == arr[right]) {
                return right;
            }
            count++;
        }

        return -1;
    }
}
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