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Solution.java
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Solution.java
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package jumpgame;
/**
* Given an array of non-negative integers, you are initially positioned at the first index of the array.
* <p>
* Each element in the array represents your maximum jump length at that position.
* <p>
* Determine if you are able to reach the last index.
* <p>
* Example 1:
* <p>
* Input: [2,3,1,1,4]
* Output: true
* Explanation: Jump 1 step from index 0 to 1, then 3 steps to the last index.
* Example 2:
* <p>
* Input: [3,2,1,0,4]
* Output: false
* Explanation: You will always arrive at index 3 no matter what. Its maximum
* jump length is 0, which makes it impossible to reach the last index.Given an array of non-negative integers, you are initially positioned at the first index of the array.
* <p>
* Each element in the array represents your maximum jump length at that position.
* <p>
* Determine if you are able to reach the last index.
* <p>
* Example 1:
* <p>
* Input: [2,3,1,1,4]
* Output: true
* Explanation: Jump 1 step from index 0 to 1, then 3 steps to the last index.
* Example 2:
* <p>
* Input: [3,2,1,0,4]
* Output: false
* Explanation: You will always arrive at index 3 no matter what. Its maximum
* jump length is 0, which makes it impossible to reach the last index.
*/
enum Index {
GOOD, BAD, UNKNOWN
}
class Solution {
/**
* Approach 3 - Dynamic Programming Bottom-up
* Time complexity : O(n^2), Space: O(n)
* <p>
* Runtime: 237 ms, faster than 31.76% of Java online submissions for Jump Game.
* Memory Usage: 42 MB, less than 23.93% of Java online submissions for Jump Game.
* TODO: Explore other solutions
*/
boolean canJump_ApproachThree(int[] nums) {
Index[] memo = new Index[nums.length];
for (int i = 0; i < memo.length; i++) {
memo[i] = Index.UNKNOWN;
}
memo[memo.length - 1] = Index.GOOD;
for (int i = nums.length - 2; i >= 0; i--) {
int furthestJump = Math.min(i + nums[i], nums.length - 1);
for (int j = i + 1; j <= furthestJump; j++) {
if (memo[j] == Index.GOOD) {
memo[i] = Index.GOOD;
break;
}
}
}
return memo[0] == Index.GOOD;
}
}