Given an array of non-negative integers, you are initially positioned at the first index of the array.
Each element in the array represents your maximum jump length at that position.
Determine if you are able to reach the last index.
For example:
A = [2,3,1,1,4], return true.
A = [3,2,1,0,4], return false.

var canJump = function(nums) {
    //记录遍历到当前节点时，其左边节点最远可到达的位置
    var rightMost = 1;
    for (var i = 0, len = nums.length; i < len; i++) {
        //如果这个节点在位置之外，那这个节点就访问不到了
        if (rightMost < i + 1) break;
        //更新最远距离
        rightMost = Math.max(rightMost, i + 1 + nums[i]);
    }
    //最远距离覆盖到最后一个节点，就能出去
    return rightMost >= len;
};