45. Jump Game II (JAVA)

佚名 6年前 (2019-05-06) 随笔 1516人围观抢沙发百度已收录

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.

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

Example:

Input: [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.

Note:

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

贪心算法，每次step都是选择最远的那个。

class Solution {
    public int jump(int[] nums) {
        if(nums.length == 1) return 0; //no need steps
        
        int start = 1; //start index of current step
        int end = nums[0]; //end index of current step
        int step = 1; //minimum steps
        int maxStep = 0; //furthest index of current step
        while(end < nums.length-1){
            for(int i = start; i <= end; i++){
                maxStep = Math.max(maxStep, nums[i]+i);
            }
            start = end+1;
            end = maxStep;
            step++;
        }
        return step;
    }
}