题解 | #找出特定体重的牛群#

知识点

二分

解题思路

先通过二分法找到与目标target相等值的下标，在再这个下标的基础上找到目标值左边与右边的边界下标。

Java题解

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) {
        // write code here
        int n = weights.length;
        int left = 0, right = n - 1;
        while(left <= right){
            int mid = left + (right - left) / 2;
            if(weights[mid] > target){
                left = mid + 1;
            } else if(weights[mid] < target) {
                right = mid - 1;
            } else {
                int start = mid, end = mid;
                while(start > 0 && weights[start - 1] == weights[start]) start--;
                while(end < n - 1 && weights[end] == weights[end + 1]) end++;
                return new int[]{start,end};
            }
        }
        return new int[]{-1,-1};
    }
}