57. Insert Interval

Description:

https://leetcode.com/problems/insert-interval/#/description

Algorithm:

Firstly, I used similar algorithm as I used in 56. Merge Intervals. The code is shown in Code1. The timing is 19ms (beats 26%). So other methods should be tried.

Use the property of ordered and non-overlap. Check one by one:

Use int start and pair to record the new merged interval, initialize start = newInterval.start, end = newInterval.end

• if intervals[i].end<start
  • push back intervals[i]
• if intervals[i].start>end
  • push back newInterval
  • push back intervals[i]
• else
  • push back min(start), max(end)

Code1:

class Solution1 {
public:
vector<Interval> insert(vector<Interval>& intervals, Interval newInterval) {
vector<Interval> result;
if (intervals.size() == 0)
{
result.push_back(newInterval);
return result;
}
Interval tmp;
map <int, int> mapping;
for (int i = 0; i < intervals.size();i++)
{
mapping[intervals[i].start] = INT_MIN;
}
mapping[newInterval.start] = INT_MIN;
for (int i = 0; i < intervals.size();i++)
{
mapping[intervals[i].start] = max(intervals[i].end, mapping[intervals[i].start]);
}
mapping[newInterval.start] = max(mapping[newInterval.start], newInterval.end);

map<int, int>::iterator it = mapping.begin();
int begin = it->first, end = it->second;
for (it = mapping.begin(); it != mapping.end();it++)
{
if (it->first <= end)
{
end = max(it->second, end);
}
else
{
tmp = Interval(begin, end);
result.push_back(tmp);
begin = it->first;
end = it->second;
}
}
tmp = Interval(begin, end);
result.push_back(tmp);
return result;
}
};

Code2:

class Solution2 {
public:
vector<Interval> insert(vector<Interval>& intervals, Interval newInterval) {
int start = newInterval.start, end = newInterval.end;
vector<Interval> res;
int inserted = false;
for (int i = 0;i<intervals.size();i++)
{
if (inserted == false)
{
if (intervals[i].start>end)
{
res.push_back(Interval(start, end));
res.push_back(intervals[i]);
inserted = true;
}
else if (intervals[i].end<start)
{
res.push_back(intervals[i]);
}
else
{
start = min(start, intervals[i].start);
end = max(end, intervals[i].end);
}
}
else
{
res.push_back(intervals[i]);
}
}
if (inserted == false) res.push_back(Interval(start, end));
return res;

}
};

Timing:

O(n)

Timing of the maps: http://blog.csdn.net/wusecaiyun/article/details/46723363