zoukankan      html  css  js  c++  java
  • Leetcode: Find Right Interval

    Given a set of intervals, for each of the interval i, check if there exists an interval j whose start point is bigger than or equal to the end point of the interval i, which can be called that j is on the "right" of i.
    
    For any interval i, you need to store the minimum interval j's index, which means that the interval j has the minimum start point to build the "right" relationship for interval i. If the interval j doesn't exist, store -1 for the interval i. Finally, you need output the stored value of each interval as an array.
    
    Note:
    You may assume the interval's end point is always bigger than its start point.
    You may assume none of these intervals have the same start point.
    Example 1:
    Input: [ [1,2] ]
    
    Output: [-1]
    
    Explanation: There is only one interval in the collection, so it outputs -1.
    Example 2:
    Input: [ [3,4], [2,3], [1,2] ]
    
    Output: [-1, 0, 1]
    
    Explanation: There is no satisfied "right" interval for [3,4].
    For [2,3], the interval [3,4] has minimum-"right" start point;
    For [1,2], the interval [2,3] has minimum-"right" start point.
    Example 3:
    Input: [ [1,4], [2,3], [3,4] ]
    
    Output: [-1, 2, -1]
    
    Explanation: There is no satisfied "right" interval for [1,4] and [3,4].
    For [2,3], the interval [3,4] has minimum-"right" start point.

    Solution 1: TreeMap,      Time complexity: O(NlogN)

    像这种在一个集合里面寻找有没有比某个数小的数,一般要么treeMap要么treeSet。Interval的题经常需要用treeMap, Data Stream as Disjoint Intervals 就是

    This implementation provides guaranteed log(n) time cost for the containsKeygetput and remove operations. 

    map.higherEntry(key) 找到的是一个entry with least key strictly greater than the given key, 所以20行要减一,因为interval.start可能跟current interval.end重合

    用map.cellingEntry(key)找的就是一个entry with least key greater than or equal to the given key

    map.lowerKey(key) Returns the greatest key strictly less than the given key, or null if there is no such key.

    map.floorKey(key) Returns the greatest key less than or equal to the given key, or null if there is no such key.

     1 /**
     2  * Definition for an interval.
     3  * public class Interval {
     4  *     int start;
     5  *     int end;
     6  *     Interval() { start = 0; end = 0; }
     7  *     Interval(int s, int e) { start = s; end = e; }
     8  * }
     9  */
    10 public class Solution {
    11     public int[] findRightInterval(Interval[] intervals) {
    12         if(intervals==null || intervals.length==0) return null;
    13         int[] res = new int[intervals.length];
    14         TreeMap<Integer, Integer> map = new TreeMap<Integer, Integer>();
    15         for (int i=0; i<intervals.length; i++) {
    16             map.put(intervals[i].start, i);
    17         }
    18         for (int i=0; i<intervals.length; i++) {
    19             Interval cur = intervals[i];
    20             Map.Entry<Integer, Integer> entry = map.higherEntry(cur.end-1);
    21             if (entry != null) {
    22                 res[i] = entry.getValue();
    23             }
    24             else res[i] = -1;
    25         }
    26         return res;
    27     }
    28 }

    Solution 2: Sweep Line Solution(未深究), Time Complexity: O(NlogN)

    https://discuss.leetcode.com/topic/65585/java-sweep-line-solution-o-nlogn

  • 相关阅读:
    Java的字节流,字符流和缓冲流对比探究
    团队作业4:第七篇Scrum冲刺博客(歪瑞古德小队)
    团队作业4:第六篇Scrum冲刺博客(歪瑞古德小队)
    团队作业4:第五篇Scrum冲刺博客(歪瑞古德小队)
    团队作业4:第四篇Scrum冲刺博客(歪瑞古德小队)
    EACCES: permission denied,mkdir … npm install 安装依赖问题解决
    100% 展示 MySQL 语句执行的神器-Optimizer Trace
    关于冲击响应的通俗理解
    struct中的对齐准则
    NIO实践-HTTP交互实现暨简版Tomcat交互内核
  • 原文地址:https://www.cnblogs.com/EdwardLiu/p/6139796.html
Copyright © 2011-2022 走看看