Leetcode: Jump Game II

Jump Game II



Similar Problems:


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.

Your goal is to reach the last index in the minimum number of jumps.

For example:
Given array A = [2,3,1,1,4]

The minimum number of jumps to reach the last index is 2. (Jump 1 step from index 0 to 1, then 3 steps to the last index.)

Note:
You can assume that you can always reach the last index.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.


## Blog link: https://code.dennyzhang.com/jump-game-ii
import sys
class Solution:
    ## Basic Ideas: greedy
    ##      maxIndex
    ##      preMaxIndex
    ## Complexity: Time O(n), Space O(n)
    def jump(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        length = len(nums)
        if length <= 1: return 0
        maxIndex, preMaxIndex, steps = 0, 0, 0
        minSteps = sys.maxsize
        for i in range(0, length-1):
            # print(i, maxIndex, preMaxIndex, length, steps, minSteps)
            # we can't jump anymore
            if i > maxIndex: break
            # all elements in current level has been examined
            if i > preMaxIndex:
                steps += 1
                preMaxIndex = maxIndex
            if maxIndex < i+nums[i]:
                maxIndex = i+nums[i]
            # already found the target
            if maxIndex >= length-1:
                minSteps = min(minSteps, steps+1)
        return minSteps

# s = Solution()
# print(s.jump([7,0,9,6,9,6,1,7,9,0,1,2,9,0,3])) # 2
# print(s.jump([2,3,1,1,4])) # 2
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