[LeetCode] 57. Insert Interval

• Problem:
• 將一個新的 interval 插入到已排序且不 overlapped 的 interval list 中, 必要時進行 merge
• Solution: 
• 先將 newInterval 依據 start 放到 interval list中
• 檢查 interval 是否需要 merge

/**
 * Definition for an interval.
 * struct Interval {
 *     int start;
 *     int end;
 *     Interval() : start(0), end(0) {}
 *     Interval(int s, int e) : start(s), end(e) {}
 * };
 */

static bool isIntersec(const Interval &a, const Interval &b)
{
    return max(a.start, b.start) <= min(a.end, b.end);
}

static Interval mergeInterval(const Interval &a, const Interval &b)
{
    return (isIntersec(a, b))? Interval(min(a.start, b.start), max(a.end, b.end)) : Interval(0, 0);
}

class Solution {
public:
    vector insert(vector& intervals, Interval newInterval) {
        vector result;
        // step 1. directly add newInterval into intervals first
        vector::iterator it;
        for (it = intervals.begin(); it < intervals.end(); it++)
        {
            if (newInterval.start < it->start)
            {
                break;
            }
        }
        intervals.insert(it, newInterval);

        // step 2. merge nearby intervals if necessary
        for (size_t i = 0; i < intervals.size(); i++){
            Interval merged(intervals[i].start, intervals[i].end);
            while (i+1 < intervals.size() && isIntersec(merged, intervals[i+1]))
            {
                merged.end = max(merged.end, intervals[i+1].end);
                i++;
            }
            result.push_back(merged);
        }
        
        return result;
    }
};