【Leetcode】【Hard】Insert Interval

Given a set of non-overlapping intervals, insert a new interval into the intervals (merge if necessary).

You may assume that the intervals were initially sorted according to their start times.

Example 1:
Given intervals [1,3],[6,9], insert and merge [2,5] in as [1,5],[6,9].

Example 2:
Given [1,2],[3,5],[6,7],[8,10],[12,16], insert and merge [4,9] in as [1,2],[3,10],[12,16].

This is because the new interval [4,9] overlaps with [3,5],[6,7],[8,10].

解题思路：

1、先用两次二分查找找到和待插入的区间有关系的区间范围；

2、将有关系的区间做处理；

3、生成新的合并后的区间并返回；

解题步骤：

代码：

/**
 * Definition for an interval.
 * struct Interval {
 *     int start;
 *     int end;
 *     Interval() : start(0), end(0) {}
 *     Interval(int s, int e) : start(s), end(e) {}
 * };
 */
class Solution {
public:
    static bool partial_order(const Interval &a, const Interval &b) {
        return a.end < b.start;
    };
    
    vector<Interval> insert(std::vector<Interval> &intervals, Interval newInterval) {
        vector<Interval>::iterator less = lower_bound(intervals.begin(), intervals.end(), newInterval, partial_order);
        vector<Interval>::iterator greater = upper_bound(intervals.begin(), intervals.end(), newInterval, partial_order);
        
        vector<Interval> answer; 
        answer.insert(answer.end(), intervals.begin(), less);
        if (less < greater) {
            newInterval.start = min(newInterval.start, (*less).start);
            newInterval.end = max(newInterval.end, (*(greater - 1)).end);
        }
        answer.push_back(newInterval);
        answer.insert(answer.end(), greater, intervals.end());
        
        return answer;
  }
};

不用lower_bound和upper_bound写的AC烂代码，留作改进：

/**
 * Definition for an interval.
 * struct Interval {
 *     int start;
 *     int end;
 *     Interval() : start(0), end(0) {}
 *     Interval(int s, int e) : start(s), end(e) {}
 * };
 */
class Solution {
public:
    vector<Interval> insert(vector<Interval>& intervals, Interval newInterval) {
        if (intervals.empty())
            return vector<Interval> (1, newInterval);
        int left = 0;
        int right = intervals.size() - 1;
        int size = intervals.size();
        int ins_start, ins_end;
        
        while (left < right) {
            int mid = (left + right) / 2;
            if (intervals[mid].end < newInterval.start)
                left = mid + 1;
            else 
                right = mid;
        }
        ins_start = left;
        
        left = left == 0 ? 0 : left - 1;
        right = intervals.size() - 1;
        while (left < right) {
            int mid = (left + right) / 2 + 1;
            if (newInterval.end < intervals[mid].start)
                right = mid - 1;
            else
                left = mid;
        }
        ins_end = right;
        
        if (ins_end == 0 && newInterval.end < intervals[0].start) {
            intervals.insert(intervals.begin(), newInterval);
            return intervals;
        }
        if (ins_start == size - 1 && newInterval.start > intervals[size - 1].end) {
            intervals.push_back(newInterval);
            return intervals;
        }
        
        vector<Interval> answer;
        answer.insert(answer.end(), intervals.begin(), intervals.begin() + ins_start);
        if (ins_start <= ins_end) {
            newInterval.start = min(newInterval.start, intervals[ins_start].start);
            newInterval.end = max(newInterval.end, intervals[ins_end].end);
        }
        answer.push_back(newInterval);
        answer.insert(answer.end(), intervals.begin() + ins_end + 1, intervals.end());
        return answer;
        
    }
};