45. Jump Game II

Description

Given an array of non-negative integers nums, you are initially positioned at the first index of the array.

Each element in the array represents your maximum jump length at that position.

Your goal is to reach the last index in the minimum number of jumps.

You can assume that you can always reach the last index.

Constraints

• 1 <= nums.length <= 1000

• 0 <= nums[i] <= 105

Approach

Links

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

Example 1

Input: nums = [2, 3, 1, 1, 4]

Output: 2

Explanation: The minimum number of jumps to reach the last index is 2. Jump 1 step from index 0 to 1, then 3 steps to the last index.

Example 2

Input: nums = [2, 3, 0, 1, 4]

Output: 2

Solutions

Solution 1

/**
 * Time complexity : 
 * Space complexity : 
 */

class Solution {
    public int jump(int[] nums) {
        if(nums == null || nums.length <= 1) {
            return 0;
        }
        int jumps = 0, reach = 0, lastReach = 0;
        
        for(int i = 0; i <= reach && i < nums.length; i++) {
            if(i > lastReach) {
                jumps++;
                lastReach = reach;
            }
            reach = Math.max(reach, nums[i]+i);
        }
        
        if(reach < nums.length-1) {
            return 0;
        }
        
        return jumps;
    }
}

Follow up