leetcode Question 39: Jump Game II

Jump Game II

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.)

Analysis:
Using greedy idea, every time get the max length. Details see the code.

Code (C++):

class Solution {
public:
    int jump(int A[], int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (n==0) {return 0;}
        if (n==1) {return 0;}
        int m=0;
        int i=0;
        int njump=0;
        while (i<n){
            m=max(m,A[i]+i);
            if (m>0) {njump++;}
            if (m>=n-1){return njump;}
            int tmp=0;
            for (int j = i+1; j<=m;j++){
                if (j+A[j]>tmp){
                    tmp=A[j]+j;
                    i=j;
                }
            }
            
        }
        return njump;
    }
};

Code (Python):

class Solution:
    # @param A, a list of integers
    # @return an integer
    def jump(self, A):
        m = 0
        i = 0
        res = 0
        if (len(A)<=1):
            return 0
        while i<len(A):
            m = max(m,A[i]+i)
            if m>0:
                res=res+1
            if m>=len(A)-1:
                return res
            tmp=0
            for j in xrange(i+1,m+1):
                if (j+A[j]>tmp):
                    tmp = j+A[j]
                    i = j
        return res