Jump Game

题意：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：两种解法，第一：从前往后进行判断，一层一层往上跳，若是最后可以越过最高层，说明每一层都可以到达；第二，从最高层下楼梯，一层一层下降，看最后能不能下降到第0层。

代码：

package com.JumpGame;

public class JumpGame {
    //从前往后推断
    public boolean canJump(int []a) {
        int maxCover = 0;
        for (int start = 0; start < a.length && start <= maxCover; start++) {
            if(start + a[start] > maxCover){
                maxCover = start + a[start];
            }
            if(maxCover > a.length) return true;
        }
        return false;
    }

    public boolean canJump2(int[] a){
        int left_most = a.length - 1;
        for (int i = a.length - 2; i >= 0; i--) {
            if(i + a[i] >= left_most)
                left_most = i ;
            if(left_most == 0) return true;
        }
        return false;
    }
    public static void main(String[] args) {
         int[] a = {3,2,1,0,4};
         JumpGame jGame = new JumpGame();
         System.out.println(jGame.canJump(a));
         System.out.println(jGame.canJump2(a));

    }

}