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:

  1. You may assume the interval’s end point is always bigger than its start point.
  2. You may assume none of these intervals have the same start point.

Example 1:

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Input: [ [1,2] ]
Output: [-1]
Explanation: There is only one interval in the collection, so it outputs -1.

Example 2:

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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:

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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.

思路

利用哈希表存储临时的访问数据并不能防止TLE。这种方法不好使。

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class Solution(object):
def findRightInterval(self, intervals):
"""
:type intervals: List[Interval]
:rtype: List[int]
"""
stats = {}
length = len(intervals)
ans = [-1] * length
for i in range(length):
cur = intervals[i].end
if (stats.has_key(cur)):
ans[i] = stats[cur]
else:
target = float('inf')
pos = -1
for j in range(length):
if (cur <= intervals[j].start):
if (target >= intervals[j].start):
target = intervals[j].start
pos = j
ans[i] = pos
stats[cur] = pos
return ans

还是利用二分法的查找来解决问题。思路其实很简单,把所有的intervals.start作为一个数组,intervals.end作为一个数组。对start数组排序,根据end数组来找和start数组里面最接近的数字。

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# Definition for an interval.
# class Interval(object):
# def __init__(self, s=0, e=0):
# self.start = s
# self.end = e
class Solution(object):
def findRightInterval(self, intervals):
"""
:type intervals: List[Interval]
:rtype: List[int]
"""
stats = {}
find = {}
length = len(intervals)
ans = [-1] * length
starts = []
for i in range(length):
find[intervals[i].start] = i
starts.append(intervals[i].start)
starts.sort()
for i in range(length):
cur = intervals[i].end
if (stats.has_key(cur)):
ans[i] = stats[cur]
else:
low = 0
high = length - 1
mid = -1
useMid = False
if (cur <= starts[-1]):
while (low + 1 < high):
mid = ( low + high ) / 2
if (starts[mid] < cur):
low = mid
elif(starts[mid] > cur):
high = mid
else:
useMid = True
break
if(useMid):
stats[cur] = find[starts[mid]]
ans[i] = find[starts[mid]]
else:
lowcur = starts[low] - cur
if (lowcur > 0):
stats[cur] = find[starts[low]]
ans[i] = find[starts[low]]
else:
stats[cur] = find[starts[high]]
ans[i] = find[starts[high]]
return ans