Leetcode 55. Jump Game

最新推荐文章于 2024-04-23 11:31:12 发布

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本文探讨了两种解决数组中跳跃问题的方法：一种是简单的递归解决方案，但可能会导致时间限制超时；另一种则通过从后向前遍历数组，设置目标位置来优化路径寻找过程，实现了高效判断是否能到达最后一个元素的目标。

Simple recursion solution but got TLE.

public class Solution {
    private boolean isJump = false;
    
    public void canJumpRecur(int cur, int k, int[] nums) {
        if (cur == nums.length-1) { isJump = true; return; }
        for (int i=1; i<=k; i++)
            if (cur+i < nums.length)
                canJumpRecur(cur+i, nums[cur+i], nums);
    }
    
    public boolean canJump(int[] nums) {
        canJumpRecur(0, nums[0], nums);
        return isJump;
    }
}

Another approach.

/**
 * Assume the length of the array is len, and the beginning target is len-1.
 * Then starting from len-2, 
 * if nums[len-2] + len-2 >= len-1 which means we can reach len-1 from len-2.
 * set len-2 as new target.
 * else check the previous index which is len-3.
 * finally if the target equals to 0 which means we can find a path from 0 to len-1.
 */ 
public class Solution {
    public boolean canJump(int[] nums) {
        int len = nums.length;
        int target = len-1;
        
        for (int i=len-2; i>=0; i--) 
            if (nums[i]+i >= target)
                target = i;
        
        return target == 0;
    }
}