题解 | #找出特定体重的牛群#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param weights int整型一维数组
     * @param target int整型
     * @return int整型一维数组
     */
    public int[] searchRange (int[] weights, int target) {
        int left = fingLeftBoundry(weights, target);
        int right = findRightBoundry(weights, target);
        if (left <= right) {
            return new int[] {left, right};
        } else {
            return new int[] {-1, -1};
        }
        // write code here
    }
    private int fingLeftBoundry(int[] weights, int target) {
        int left = 0, right = weights.length - 1;
        int leftBoundry = -1;
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (weights[mid] == target) {
                leftBoundry = mid;
                right = mid - 1;
            } else if (weights[mid] < target) {
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }
        return leftBoundry;
    }
    private int findRightBoundry(int[] weights,int target){
        int left=0,right=weights.length-1;
        int rightBoundry =-1;
        while(left<=right){
            int mid = left + (right-left)/2;
            if(weights[mid]==target){
                rightBoundry = mid;
                left = mid+1;
            }else if(weights[mid]<target){
                right = mid-1;
            }else{
                left = mid+1;
            }
        }
        return rightBoundry;
    }
}

首先使用两次二分查找分别找到特定体重牛的左边界和右边界，然后根据找到的左边界和右边界返回结果。左边界的查找函数 findLeftBoundary 找到第一个等于目标体重的位置，右边界的查找函数 findRightBoundary 找到最后一个等于目标体重的位置。如果左边界小于等于右边界，说明存在特定体重的牛，返回起始位置和结束位置，否则返回 [-1, -1] 表示没有找到。