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.

Have you met this question in a real interview? 

Yes

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.)

java不会超时，但是python会超时。by 贪心法不会，所以不写最优解了

java

public class Solution {
    /*
     * @param A: A list of integers
     * @return: An integer
     */
    public int jump(int[] A) {
        // write your code here
        if (A == null || A.length == 0) {
            return 0;
        }
        int[] f = new int[A.length];
        for (int i = 0; i < A.length; i++) {
            f[i] = Integer.MAX_VALUE;
        }
        f[0] = 0;
        for (int i = 1; i < A.length; i++) {
            for (int j = 0; j < i; j++) {
                if (f[j] != Integer.MAX_VALUE && j + A[j] >= i) {
                    f[i] = Math.min(f[i], 1 + f[j]);
                }
            }
        }
        return f[A.length - 1];
    }
}

python

class Solution:
    """
    @param: A: A list of integers
    @return: An integer
    """
    def jump(self, A):
        # write your code here
        if A is None or len(A) == 0:
            return 0
        res = [float('inf')] * len(A)
        res[0] = 0
        for i in range(1, len(A)):
            for j in range(i):
                if res[j] != float('inf') and A[j] + j >= i:
                    res[i] = min(res[i], res[j] + 1)
        return res[-1]