查看“︁55.Jump Game”︁的源代码

=Description=
{{LeetCode
|id=jump-game
|no=55
|difficulty=Medium
|category=Dynamic Programming
|collection=Top 150
|title=Jump Game
|summary=You are given an integer array nums. You are initially positioned at the array's first index, and each element in the array represents your maximum jump length at that position.

Return true if you can reach the last index, or false otherwise.}}

Example 1:

<syntaxhighlight lang="bash">
Input: nums = [2,3,1,1,4]
Output: true
</syntaxhighlight>
Explanation: Jump 1 step from index 0 to 1, then 3 steps to the last index.
Example 2:

<syntaxhighlight lang="bash">
Input: nums = [3,2,1,0,4]
Output: false
</syntaxhighlight>
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.

=Solution=
==1D DP==
{{Submission|runtime=418ms|memory=43.4MB|rp=7.2|mp=97.69}}

<syntaxhighlight lang="java">
class Solution {
    public boolean canJump(int[] nums) {
        /*
            [2,3,1,1,4]
             1 1 2 2 2
         */
        int []dp = new int[nums.length];
        dp[0] = 1;
        for(int i = 0; i < nums.length; i++) {
            for(int j = 1; j <= nums[i]; j++){
                if(i+j >= dp.length) break;
                dp[i+j]++;
            }
                
        }
        for(int i = 0; i < dp.length; i++) {
            if(dp[i] == 0) return false;
        }
            
        return true;
    }
}
</syntaxhighlight>

==1D DP 2==
{{Submission|runtime=76ms|memory=43.85MB|rp=17.86|mp=83.06}}

<syntaxhighlight lang="java">
class Solution {
    public boolean canJump(int[] nums) {
        boolean []dp = new boolean[nums.length];
        dp[0] = true;
        for(int i = 0; i <nums.length; i++) {
            if(!dp[i]) return false;
            for(int j = 1; j <= nums[i]; j++) {
                int next = i + j;
                if(next >= dp.length) break;
                if(next == nums.length -1) return true; // reach end already
                dp[next] = true;
            }
        }
        return dp[nums.length-1];
    }
}
</syntaxhighlight>

== Greedy ==
{{Submission|runtime=2ms|memory=44.02MB|rp=80.65|mp=69.15}}
<syntaxhighlight lang="bash">
class Solution {
    public boolean canJump(int[] nums) {
        // keep track of the current max reachable position of each step
        int reachable = 0;
        for(int i = 0; i < nums.length; i++) {
            if(i > reachable) return false;
            reachable = Math.max(reachable, i + nums[i]);
        }
        return true;
    }
}
</syntaxhighlight>

[[Category:Algorithm]]
[[Category:Dynamic Programming]]
[[Category:Greedy]]
[[Category:LeetCode]]