57. Insert Interval

1.問題

• 給予一個不重疊的intervals list並插入一個新的interval, 必要時必須融合intervals

2.想法

• 提問: interval間是否已排序?

• function header, parameter

• test input

• 說明想法 (同56.Merge Interval)

  • 必須先排序Interval: overwrite sort operation

  //define sort operation
  struct IntervalKey {
          inline bool operator() (const Interval &pLHS, const Interval &pRHS) {
              return pLHS.start < pRHS.start;
          }
      };
  
  //sort vector
  sort(intervals.begin(), intervals.end(), IntervalKey());

  • 比較Interval[i]與interval[i - 1]:

    • 如果有重疊, 則讓interval[cnt].end = interval[i].end

    • 不然則將interval[i]加入

• 測試計算複雜度

3.程式碼

/**
 * 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:
    struct IntervalKey{
        inline bool operator() (const Interval& pLHS, const Interval& pRHS) {
            return pLHS.start < pRHS.start;
        }
    };
    vector<Interval> insert(vector<Interval>& intervals, Interval newInterval) {
        vector<Interval> res;
        int size = intervals.size();
        if (size == 0) {
            res.push_back(newInterval);
            return res;
        }
        intervals.push_back(newInterval);
        sort(intervals.begin(), intervals.end(), IntervalKey());
        int cnt = 0;
        for (int i = 1; i < size + 1; i++) {
            if (intervals[i].start <= intervals[cnt].end && intervals[i].end >= intervals[cnt].start) {
                intervals[cnt].end = max(intervals[cnt].end, intervals[i].end);
            } else {
                ++cnt;
                intervals[cnt].start = intervals[i].start;
                intervals[cnt].end = intervals[i].end;
            }
        }
        
        res.assign(intervals.begin(), intervals.begin() + cnt + 1);
        return res;
    }
};