Leetcode-228 Summary Ranges

Given a sorted integer array without duplicates, return the summary of its ranges.

For example, given [0,1,2,4,5,7], return ["0->2","4->5","7"].

Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

题解：两个指针 start, end.  如果nums[end+1] = nums[end]+1, 就移动end指针, 否则, 插入字符串nums[start]->nums[end]. 

/**
 * @param {number[]} nums
 * @return {string[]}
 */
var summaryRanges = function(nums) {
    var str=new Array();
    var start,end,s,e;
    var len = nums.length;
    if(len<1 || nums===null){
        return str;
    }
    str[0]="";
    start=0;
    var k=0;
    end=0;
    while(end<len){
        str[k]="";
        if(end+1<len && nums[end+1]===nums[end]+1){
            end++;
        }
        else{
            if(start === end){
                str[k++]+=nums[start];
            }
            else{
                str[k++]+=nums[start]+"->"+nums[end];
            }
            end++;
            start=end;
        }
    }
    
    return str;
};