55. Jump Game

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.

可以从终点向前遍历，同时累加一个记步。如果当前的数大于等于记步，说明从这个点可以到达之前的记步处，重置记步数为0，如果小于则说明不能到达，记步数加1，遍历下一个数。代码如下：

public class Solution {
    public boolean canJump(int[] nums) {
        boolean res = false;
        int count = 0;
        for (int i = nums.length - 1; i >= 0; i --) {
            if (nums[i] >= count) {
                res = true;
                count = 0;
            } else {
                res = false;
            }
            count ++;
        }
        return res;
    }
}

当然也可以从前向后遍历，设一个reach数，从前向后遍历数组，reach取i+nums[i]和reach较大的一个。如果i大于reach了，说明到不了，停止遍历，返回false，如果i等于n，说明可以到，返回true。代码如下：

bool canJump(int A[], int n) {
    int i = 0;
    for (int reach = 0; i < n && i <= reach; ++i)
        reach = max(i + A[i], reach);
    return i == n;
}