55.Jump-Game

55. Jump Game

题目地址

https://www.jiuzhang.com/solutions/jump-game

题目描述

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.

代码

Approach #1: Dynamic Programming

public class Solution {
  public boolean canJump(int[] A) {
    boolean[] f = new boolean[A.length];
    f[0] = true;

    for (int i = 1; i < A.length; i++) {
      for (int j = 0; j < i; j++) {
        if (f[j] && j + A[j] >= i) {
          f[i] = true;
          break;
        }
      }
    }
    return f[A.length - 1];
  }
}

Approach #2: Greedy

public class Solution {
  public boolean canJump(int[] A) {
    if (A == null || A.length == 0) {
        return false;
    }

    int farthest = A[0];
    for (int i = 1; i < A.length; i++) {
        if (i <= farthest && A[i] + i >= farthest) {
            farthest = A[i] + i;
        }
    }

    return farthest >= A.length - 1;
  }
}

class Solution {
  public boolean canJump(int[] nums) {
    int n = nums.length;
    int maxPos = nums[0];

    for (int i = 1; i < n; i++) {
      if (maxPos < i) {
        return false;
      }
      maxPos = Math.max(maxPos, nums[i] + i);
    }
    return true;
  }
}