贪心

55. Jump Game(贪心)

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

 

45. 跳跃游戏 II

class Solution {
public:
//The main idea is based on greedy. Let's say the range of the current jump is [curBegin, curEnd], curFarthest is the farthest point that all points in [curBegin, curEnd] can reach. Once the current point reaches curEnd, then trigger another jump, and set the new curEnd with curFarthest, then keep the above steps, as the following:

    int jump(vector<int>& nums) 
    {
        int max_far = 0;// 目前能跳到的最远位置
        int step = 0;   // 跳跃次数
        int end = 0;    // 上次跳跃可达范围右边界（下次的最右起跳点）
        for (int i = 0; i < nums.size() - 1; i++)
        {
            max_far = std::max(max_far, i + nums[i]);
            // 到达上次跳跃能到达的右边界了
            if (i == end)
            {
                end = max_far;  // 目前能跳到的最远位置变成了下次起跳位置的有边界
                step++;         // 进入下一次跳跃
            }
        }
        return step;
    }
};