55, Jump Game

I Problem

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
Input: nums = [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
Input: nums = [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.

Constraints

• 1 <= nums.length <= 10⁴
• 0 <= nums[i] <= 10⁵

Related Topics

• Array
• Dynamic Programming
• Greedy

II Solution

Approach 1: Greedy

pub fn can_jump(nums: Vec<i32>) -> bool {
    let max_idx = nums.len() - 1;
    let mut rightmost = 0;

    for i in 0..=max_idx {
        if i <= rightmost {
            rightmost = std::cmp::max(rightmost, i + nums[i] as usize);
            if rightmost >= max_idx {
                return true;
            }
        }
    }

    false
}

public boolean canJump(int[] nums) {
    int maxIdx = nums.length - 1;
    int rightmost = 0;

    for (int i = 0; i <= maxIdx; i++) {
        if (i <= rightmost) {
            rightmost = Math.max(rightmost, i + nums[i]);
            if (rightmost >= maxIdx) {
                return true;
            }
        }
    }

    return false;
}

func canJump(nums []int) bool {
    maxIdx := len(nums) - 1
    rightmost := 0
    
    for i := 0; i <= maxIdx; i++ {
        if i <= rightmost {
            rightmost = max(rightmost, i+nums[i])
            if rightmost >= maxIdx {
                return true
            }
        }
    }
    
    return false
}

Approach 2: Reverse Traversal

pub fn can_jump(nums: Vec<i32>) -> bool {
    let mut jump_len = 1;

    for i in (0..nums.len() - 1).rev() {
        if nums[i] >= jump_len {
            jump_len = 1;
        } else {
            jump_len += 1;
        }
    }

    jump_len == 1
}

public boolean canJump(int[] nums) {
    int jumpLen = 1;

    for (int i = nums.length - 2; i >= 0; i--) {
        if (nums[i] >= jumpLen) {
            jumpLen = 1;
        } else {
            jumpLen++;
        }
    }

    return jumpLen == 1;
}

func canJump(nums []int) bool {
    jumpLen := 1

    for i := len(nums) - 2; i >= 0; i-- {
        if nums[i] >= jumpLen {
            jumpLen = 1
        } else {
            jumpLen++
        }
    }

    return jumpLen == 1
}