No.207&210 - LeetCode[55] Jump Game & [45] Jump Game II - 数组走到最后的最少步骤

纯dp会超时

/*
 * @lc app=leetcode id=45 lang=cpp
 *
 * [45] Jump Game II
 */

// @lc code=start
class Solution {
public:
    int jump(vector<int>& nums) {
        int N = nums.size();
        vector<int> dp(N,-1);
        for(int i=0;i<N;i++){
            dp[i] = i;
        }
        for(int i=0;i<N;i++){
            for(int j=i+1;j<min(N,i+1+nums[i]);j++){
                dp[j] = min(dp[j],dp[i]+1);
            }
        }
        return dp[N-1];
    }
};
// @lc code=end

像这种只往前走，求最短路径的，可以考虑游标+BFS：

/*
 * @lc app=leetcode id=45 lang=cpp
 *
 * [45] Jump Game II
 */

// @lc code=start
class Solution {
public:
    int jump(vector<int>& nums) {
        int N = nums.size();
        if(N <= 1) return 0;
        queue<pair<int,int>> q;
        q.push(make_pair(0,0)); // loc,level
        int cur = 1;            // cursor
        while(!q.empty()){
            int loc = q.front().first;
            int level = q.front().second;
            for(int i=cur;i<min(N,loc+1+nums[loc]);i++){
                q.push(make_pair(i,level+1));
                if(i == N-1){
                    return level+1;
                }
            }
            cur = min(N,loc+1+nums[loc]);
            q.pop();
        }
        return -1;
    }
};
// @lc code=end

/*
 * @lc app=leetcode id=55 lang=cpp
 *
 * [55] Jump Game
 */

// @lc code=start
class Solution {
public:
    bool canJump(vector<int>& nums) {
        int N = nums.size();
        int cur = 0;
        int ans = 0;
        queue<int> q;
        q.push(0);
        while(!q.empty()){
            int now = q.front();
            for(int i=cur+1;i<=min(N-1,now+nums[now]);i++){
                q.push(i);
            }
            cur = max(cur,now + nums[now]);
            q.pop();
        }
        if(cur >= N-1) return true;
        return false; 
    }
};
// @lc code=end