Jump Game

Problem 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.

Solutions

The idea is obvious. We use dynamic programming technique, and scan the array forward or backward. Needless to say, the code has just a few lines.
I. Scanning Backward

class Solution:
    # @param {integer[]} nums
    # @return {boolean}
    def canJump(self, nums):
        n = len(nums)
        last = n-1
        for i in range(2,n+1):
            if n-i + nums[-i] >= last:
                last = n-i
        return last == 0

II. Scanning Forward

class Solution:
    # @param {integer[]} nums
    # @return {boolean}
    def canJump(self, nums):
        reachable = 0
        for i in range(len(nums)):
            if i > reachable: return False
            reachable = max(reachable, i+nums[i])
        return True