class Solution {public:    bool canJump(int A[], int n) {        if (A == NULL || n < 1) return false;        vector<int> sum(n, 0);        int jump = A[n-1];                for (int i=n-2; i>=0; i--) {            jump = A[i];            if (i + jump >= n - 1) {                sum[i] = sum[i+1] + 1;                continue;            }            int region = sum[i + 1] - sum[i + jump + 1];            sum[i] = sum[i+1] + (region > 0);        }                if (jump >= n-1) {            return true;        } else {            return sum[0] - sum[jump] > 0;        }    }};