SOURCE

class RangeList {
    constructor() {
        this.rangeList = [];
    }
    /**
    * Adds a range to the list
    * @param {Array<number>} range - Array of two integers that specify
    beginning and end of range.
    */
    add(range) {
       if(this.valid(range)) {
           let [start, end] = range;
           
           if(start < end) {
               let length = this.rangeList.length;
               if(length === 0) {
                   this.rangeList.push(range);
                   return;
               }

               let newRangeList = [];
               let hasPush = false;
               for(let i = 0; i < length; i++) {
                   let [curStart, curEnd] = this.rangeList[i];
                    
                   if(curStart > end) {
                       newRangeList.push(this.rangeList[i]);
                   }
                   else {
                     if(start > curEnd) {
                         newRangeList.push(this.rangeList[i]);
                     }   
                     else {
                         hasPush = true;
                         this.insert(curStart, curEnd, start, end, newRangeList)
                    
                     }
                   }
               }
               if(!hasPush) {
                    newRangeList.push(range);
               }
               this.rangeList = newRangeList;
           }
       }
    }
    /**
     * combine range
     * egg: [1, 8] ,then add [3, 10], result is [1, 10]
     */
    insert(curStart, curEnd, addStart, addEnd, newRangeList) {
        let start = Math.min(curStart, addStart);
        let end = Math.max(curEnd, addEnd);
        let i = newRangeList.length - 1;
        while(i >= 0) {
            if(start <= newRangeList[i][1] && start >= newRangeList[i][0]) {
                newRangeList[i][1] = end;
                return;
            }
            else if(start < newRangeList[i][0]){
                break;
            }
            i--;
        }
        newRangeList.push([start, end]);
    }
    /**
    * Removes a range from the list
    * @param {Array<number>} range - Array of two integers that specify
    beginning and end of range.
    */
    remove(range) {
        if(this.valid(range)) {
            let [removeStart, removeEnd] = range;

            if(removeStart < removeEnd) {
                let length = this.rangeList.length;
                let newRange = [];
                for(let i = 0; i < length; i++) {
                    let [curStart, curEnd] = this.rangeList[i];
                    
                    // egg: [5, 10], then remove [8, 20], result is [5, 8]
                    if(removeStart > curStart && removeStart < curEnd && removeEnd > curEnd) {
                        newRange.push([curStart, removeStart]);
                    }
                    // egg: [5, 10], then remove [5, 8] or remove [8, 10] or remove [6,8], has 3 cases
                    else if(removeStart >= curStart && removeEnd <= curEnd) {
                        if(curStart === removeStart) {
                            if(curEnd !== removeEnd) {
                                newRange.push([removeEnd, curEnd]);
                            }
                        }
                        else if(curEnd === removeEnd) {
                            newRange.push([curStart, removeStart]);
                        }
                        else if(curStart !== removeStart && curEnd !== removeEnd) {
                           newRange.push([curStart, removeStart],[removeEnd, curEnd]);
                        }
                    }
                    // egg: [5, 10], then remove [1, 8], result is [8, 10]
                    else if(removeStart < curStart && removeEnd > curStart && removeEnd <= curEnd) {
                        if(removeEnd !== curEnd) {
                             newRange.push([removeEnd, curEnd])
                        }
                    }
                    else if(removeEnd <= curStart || removeStart > curEnd) {
                          newRange.push(this.rangeList[i]);
                    }
                }
                this.rangeList = newRange;
            }

        }
    }
    valid(range) {
        if(Array.isArray(range) && range.length === 2) {
            return true;
        }
        return false;
    }
    
    /**
    * Prints out the list of ranges in the range list
    */
    print() {
        let res = '';
        for(let [start, end] of this.rangeList) {
            res += `[${start}, ${end}) `
        }
        console.log(res);
        return res;
    }
}

const rl = new RangeList();
rl.add([1, 5]);
rl.print();
// Should display: [1, 5)
rl.add([10, 20]);
rl.print();
// Should display: [1, 5) [10, 20)
rl.add([20, 20]);
rl.print();
// Should display: [1, 5) [10, 20)
rl.add([20, 21]);
rl.print();
// Should display: [1, 5) [10, 21)
rl.add([2, 4]);
rl.print();
// Should display: [1, 5) [10, 21)
rl.add([3, 8]);
rl.print();
// Should display: [1, 8) [10, 21)
rl.remove([10, 10]);
rl.print();
// Should display: [1, 8) [10, 21)
rl.remove([10, 11]);
rl.print();
// Should display: [1, 8) [11, 21)
rl.remove([15, 17]);
rl.print();
// Should display: [1, 8) [11, 15) [17, 21)
rl.remove([3, 19]);
rl.print();
// Should display: [1, 3) [19, 21)