LeetCode34-查找排序数组中元素位置【Java】

LeetCode34-查找排序数组中元素位置【Java】

• 给定一个按照升序排列的整数数组 nums，和一个目标值 target。找出给定目标值在数组中的开始位置和结束位置。如果数组中不存在目标值 target，返回 [-1, -1]。

• 例 ：
  输入：nums = [5,7,7,8,8,10], target = 8
  输出：[3,4]

• 输入：nums = [5,7,7,8,8,10], target = 6
  输出：[-1,-1]

public class LC34_FindElement {
    public static void main(String[] args) {
        int[] array = {1,2,5,5,9,21};
        int[] ints = FindElement(array, 1);
        int[] ints1 = FindElement_plus(array, 1);
        System.out.println("["+ints[0] + "," + ints[1] + "]");
        System.out.println("["+ints1[0] + "," + ints1[1] + "]");
    }
    
    private static int[] FindElement(int[] nums, int target) {
        //定义一个结果集存储开始和结束下标
        int[] result = {-1,-1};
        //定义一个右指针
        int left = 0;
        int right = nums.length-1;
        for (; left < nums.length; left++) {
            if (nums[left] == target) {
                result[0] = left;
                for (; left <= right ; right--) {
                    if (nums[right] == target) {
                        result[1] = right;
                        return result;
                    }
                }
            }
        }
        return result;
    }

---

 
    private static int[] FindElement_plus(int[] nums, int target) {

        //定义一个结果集
        int[] result = {-1,-1};
        //true代表寻找左边界，false代表寻找右边界
        result[0] = binarySearch(nums,target,true);
        result[1] = binarySearch(nums,target,false);
        return result;
    }
    private static int binarySearch(int[] nums, int target, boolean b) {
        int res = -1;
        //定义一个左指针
        int left = 0;
        //定义一个右指针
        int right = nums.length-1;
        while (left <= right) {
            //定义一个中间指针
            int mid = (left + right) / 2;
            if (nums[mid] > target) {
                right = mid -1;
            } else if ( nums[mid] < target ) {
                left = mid + 1;
            } else if ( nums[mid] == target ) {
                res = mid;
                if (b) {
                    //寻找左边界，right = mid-1 将整个寻找的区域向左移动
                    right = right - 1;

                } else {
                    //寻找右边界，left = mid+1 将整个寻找的区域向右移动
                    left = left + 1;
                }
            }
        }
        return res;
    }
}