[LeetCode] 55. Jump Game

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Problem

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

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

Determine if you are able to reach the last index.

Example 1:

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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:

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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.

Explanation

  1. First we create a variable max = 0 to record the maximum position we can reach. Then we iterate the array, update max = max(max, i+nums[i]), if max >= nums[len(nums)-1], we return true. Else if i > max, we break out the loop and return false.

Solution

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class Solution {
    public boolean canJump(int[] nums) {
        int max = 0;
        for (int i = 0; i < nums.length && i <= max; i++) {
            max = Math.max(max, nums[i]+i);
            if (max >= nums.length-1) return true;
        }
        return false;
    }
}