55. Jump Game

题目链接：https://leetcode.com/problems/jump-game/#/description

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.

思路：从头遍历每个点，首先判断这个点是不是在目前最远可达的范围内，如果是，判断这个点可以到达的最远距离，如果比已有的最远距离大，则更新最远距离。如果最远距离超过数组最后一位，那么返回true。如果遍历结束还没有返回就说明不能跳到最后一个，直接返回false。

class Solution {
public:
    bool canJump(vector<int>& nums) {
        int farpos = nums[0];
        int n = nums.size();
        if(farpos >= n-1)
            return true;
        for(int i = 1; i < n; ++i){
            if(i <= farpos)
                farpos = max(farpos, i+nums[i]);
            if(farpos >= n-1)
                return true;
        }
        return false;
    }
};