55. Jump Game (Medium)

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.

For example: A = [2,3,1,1,4], return true.

A = [3,2,1,0,4], return false.

Solution: Greedy

version 1: 22ms

class Solution {
public:
    bool canJump(vector<int>& nums) {
        int i = 0;
        for (int reach = 0; i < nums.size() && i <= reach; ++i) {
            reach = max(reach,i+nums[i]);
        }
        return i == nums.size();
    }
};

version 2: backtracking 22ms

class Solution {
public:
    bool canJump(vector<int>& nums) {
        int lastPos = nums.size() - 1;
        for (int i = nums.size()-1; i >= 0; --i) {
            if (i+nums[i] >= lastPos) lastPos = i;
        }
        return lastPos == 0;
    }
};