LeetCode-JumpGameII

2019-11-14 14:54:06

字體：大中小

來源：轉載

供稿：網(wǎng)友

題目：

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.

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

For example:
Given array A = [2,3,1,1,4]

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.)

Subscribe to see which companies asked this question

思路：

1）用一個dp數(shù)組來記錄到達當前位置的最小步數(shù)

package dp;public class JumpGameII {    public int jump(int[] nums) {                int len = nums.length;        int[] dp = new int[len];        for (int i = 0; i < len; ++i)            dp[i] = Integer.MAX_VALUE;        dp[0] = 0;        // In order to save time, we don't visit the elements which already been visited.        int start = 1;        for (int i = 0; i < len - 1; ++i) {            start = go(i, nums[i], start, dp);        }                return dp[len-1];    }        // Get next start position.    private int go(int current, int step, int start, int[] dp) {        int i = start;        for (; i <= current + step && i < dp.length; ++i) {            if (dp[i] > dp[current] + 1)                dp[i] = dp[current] + 1;        }                return i;    }        public static void main(String[] args) {        // TODO Auto-generated method stub        int[] nums = { 2,3,1,1,4 };        JumpGameII j = new JumpGameII();        System.out.println(j.jump(nums));    }}

2）不用數(shù)組，就直接往前移動，第一次掃走一步能到的地方，第二次掃走二步能到的地方，在這個過程中，只要碰到了最后一個位置，就終止，證明是最小步數(shù)。

package dp;public class JumpGameII {    public int jump(int[] nums) {        int len;         if ((len = nums.length) == 1) return 0;        int count = 0;        int start = 0;        int end = 0;        while (end < len) {            int mostRight = 0;            ++count;            for (int j = start; j <= end; ++j) {                if (j + nums[j] >= len - 1)                    return count;                if (j + nums[j] > mostRight)                    mostRight = j + nums[j];            }                        start  = end + 1;            end = mostRight;        }                return count;    }        public static void main(String[] args) {        // TODO Auto-generated method stub        int[] nums = { 2,3,1,1,4 };        JumpGameII j = new JumpGameII();        System.out.println(j.jump(nums));    }}