(字符串)较大分组位置

/**
 * @param {string} s
 * @return {number[][]}
 */
var largeGroupPositions = function(s) {
    var result = [];
    var start = 0;
    var end = 1;
    while(s[end]){
        while(s[end] == s[start]){
            end++
        }
        if(end - start >=3){
            result.push([start,end-1])
        }
        start = end;
        end = start + 1;
    }
    return result;
};