[LeetCode] Jump Game

This problem has a very concise solution in this link, just 4-lines. The code is rewritten below.

class Solution {
public:
    bool canJump(vector<int>& nums) {
        int i = 0, n = nums.size();
        for (int r = 0; i < n && i <= r; i++)
            r = max(r, i + nums[i]);
        return i == n;
    }
};

The above code can be further optimized by avoiding unnecessary checks. Once we are able to reach the last position, we are already done.

class Solution {
public:
    bool canJump(vector<int>& nums) {
        int i = 0, r = 0, n = nums.size();
        for (; i < n && i <= r && r < n - 1; i++)
            r = max(r, i + nums[i]);
        return r >= n - 1;
    }
};

Or we can rewrite the code a bit longer to make the idea obvious.

class Solution {
public:
    bool canJump(int A[], int n) {
        int start = 0, end = 0;
        while(start <= end && end < n - 1) { 
            end = max(end, start + A[start]);
            start++;
        }
        return end >= n - 1;
    }
};