[LintCode] Longest Increasing Continuous subsequence II - Acjx - 博客园


[LintCode] Longest Increasing Continuous subsequence II - Acjx - 博客园
http://shibaili.blogspot.com/2015/08/day-120-longest-increasing-subsequence.html
Give you an integer matrix (with row size n, column size m),find the longest increasing continuous subsequence in this matrix. (The definition of the longest increasing continuous subsequence here can start at any row or column and go up/down/right/left any direction).
Example
Given a matrix:
[
  [1 ,2 ,3 ,4 ,5],
  [16,17,24,23,6],
  [15,18,25,22,7],
  [14,19,20,21,8],
  [13,12,11,10,9]
]
return 25
这道题使用dfs+dp,在dfs时更新状态,状态转移方程为 dp[(i,j)] = max(dp[(smaller neibors of all)])  + 1,来看代码:

O(nm) time and memory.
-------------------------------------------------- 
以每一点为path的起始,它所得到最长递增数列都是恒定的
所以用memoization即可

https://www.cnblogs.com/lz87/p/6936104.html
多重循环DP遇到了困难:  从上到下循环不能解决问题, 初始状态找不到.  我们可以用暴力搜索从大往小的搜索.
Follow up questions
Q: Can you optimize the memory usage like some other dynamic programming problems?
A: No, since to calculate dp[x][y], we need all its 4 neighbors' result, so we can't use less memory. Also, search memoization is 
hard to optimize memory usage even if we can. This is the downside of using top down memoization search compared to 
bottom up typical dynamic programming.

Q: Can you reconstruct one optimal solution? 
A: Easy. Pick one largest dp[x][y] if there are more than one. Then starting from this dp[x][y] to backtrack its neighbors of value dp[x][y] - 1, 
do this until we find a dp[i][j] = 1.


X. DFS+Cache
https://www.jianshu.com/p/1587a3385dfe
In dynamic programming, state i was computed from state i - 1 as usual. BUT, when you try to compute state i from state i +1, this turns out to be a DFS search.
The trick is that the path must fit in increasing order, which makes repeated visiting impossible. It is even an easier DFS search, isn't it?

    int dfs(vector<vector<int>>& A,vector<vector<int>> &dp,int row,int col) {
        if (dp[row][col] != 0) return dp[row][col];
        if (row + 1 < A.size() && A[row + 1][col] > A[row][col]) {
            dp[row][col] = max(dp[row][col],dfs(A,dp,row + 1,col));
        }
        if (row - 1 >= 0 && A[row - 1][col] > A[row][col]) {
            dp[row][col] = max(dp[row][col],dfs(A,dp,row - 1,col));
        }
        if (col - 1 >= 0 && A[row][col - 1] > A[row][col]) {
            dp[row][col] = max(dp[row][col],dfs(A,dp,row,col - 1));
        }
        if (col + 1 < A[0].size() && A[row][col + 1] > A[row][col]) {
            dp[row][col] = max(dp[row][col],dfs(A,dp,row,col + 1));
        }
         
        dp[row][col]++;
        return dp[row][col];
    }
      
    int longestIncreasingContinuousSubsequenceII(vector<vector<int>>& A) {
        // Write your code here
        if (A.size() == 0) return 0;
        int m = A.size(), n = A[0].size();
        vector<vector<int>> dp(m,vector<int>(n,0));
        int longest = 0;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (dp[i][j] == 0) {
                    dp[i][j] = dfs(A,dp,i,j);
                }
                longest = max(longest,dp[i][j]);
            }
        }
         
        return longest;
    }
X. 遍历,所有点按高度排序
struct Dot {
        int row;
        int col;
        int height;
        Dot(int x,int y,int h):row(x),col(y),height(h) {
        }
    };
class Solution {
public:
    static bool cmp(const Dot &d1,const Dot &d2) {
        return d1.height < d2.height;
    }
    /**
     * @param A an integer matrix
     * @return  an integer
     */
    int longestIncreasingContinuousSubsequenceII(vector<vector<int>>& A) {
        // Write your code here
        if (A.size() == 0) return 0;
        int m = A.size(), n = A[0].size();
        vector<vector<int>> len(m,vector<int>(n,0));
        vector<Dot> dots;
         
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                Dot d(i,j,A[i][j]);
                dots.push_back(d);
            }
        }
         
        sort(dots.begin(),dots.end(),cmp);
        int longest = 0;
        for (int i = 0; i < dots.size(); i++) {
            if (dots[i].row + 1 < m && A[dots[i].row + 1][dots[i].col] > dots[i].height
                && len[dots[i].row + 1][dots[i].col] < len[dots[i].row][dots[i].col] + 1) {
                len[dots[i].row + 1][dots[i].col] = len[dots[i].row][dots[i].col] + 1;
            }
             
            if (dots[i].col + 1 < n && A[dots[i].row][dots[i].col + 1] > dots[i].height
                && len[dots[i].row][dots[i].col + 1] < len[dots[i].row][dots[i].col] + 1) {
                len[dots[i].row][dots[i].col + 1] = len[dots[i].row][dots[i].col] + 1;
            }
             
            if (dots[i].row - 1 >= 0 && A[dots[i].row - 1][dots[i].col] > dots[i].height
                && len[dots[i].row - 1][dots[i].col] < len[dots[i].row][dots[i].col] + 1) {
                len[dots[i].row - 1][dots[i].col] = len[dots[i].row][dots[i].col] + 1;
            }
             
            if (dots[i].col - 1 >= 0 && A[dots[i].row][dots[i].col - 1] > dots[i].height
                && len[dots[i].row][dots[i].col - 1] < len[dots[i].row][dots[i].col] + 1) {
                len[dots[i].row][dots[i].col - 1] = len[dots[i].row][dots[i].col] + 1;
            }
        }
         
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                longest = max(longest,len[i][j]);
            }
        }
         
        return longest + 1;
    }
};
https://codesolutiony.wordpress.com/2015/05/25/lintcode-longest-increasing-continuous-subsequence-ii/
    public int longestIncreasingContinuousSubsequenceII(int[][] A) {
        int res = 0;
        if (A == null || A.length == 0 || A[0].length == 0) {
            return res;
        }
        int[][] store = new int[A.length][A[0].length];
        for (int i = 0; i < A.length; i++) {
            for (int j = 0; j < A[0].length; j++) {
                if (store[i][j] == 0) {
                    res = Math.max(res, dfs(A, store, i, j));
                }
            }
        }
        return res;
    }
    private int dfs(int[][] a, int[][] store, int i, int j) {
        if (store[i][j] != 0) {
            return store[i][j];
        }
        int left = 0, right = 0, up = 0, down = 0;
        if (j + 1 < a[0].length && a[i][j+1] > a[i][j]) {
            right = dfs(a, store, i, j+1);
        }
        if (j > 0 && a[i][j-1] > a[i][j]) {
            left = dfs(a, store, i, j-1);
        }
        if (i + 1 < a.length && a[i+1][j] > a[i][j]) {
            down = dfs(a, store, i+1, j);
        }
        if (i > 0 && a[i-1][j] > a[i][j]) {
            up = dfs(a, store, i-1, j);
        }
        store[i][j] = Math.max(Math.max(up, down), Math.max(left, right)) + 1;
        return store[i][j];
    }
Longest Increasing Continuous subsequence I
[LintCode] Longest Increasing Continuous subsequence
Dynamic Programming, Time complexity = O(n^2)
f[i] = max(f[j] + 1) for all j < i and n[i] > n[j]
int longestIncreasingSubsequence(vector<int> nums) {
        // write your code here
        auto size = nums.size();
        if (size==0) return 0;
        vector<int> f(size, 1);
        for(auto i=0;i<size;++i)
            for(auto j=0;j<i;++j)
                if(nums[i]>=nums[j])
                    f[i] = max(f[i], f[j]+1);
                
        return *std::max_element(f.begin(), f.end());
    }
Nlogn
http://www.geeksforgeeks.org/longest-monotonically-increasing-subsequence-size-n-log-n/
http://www.csie.ntnu.edu.tw/~u91029/LongestIncreasingSubsequence.html
http://codeanytime.blogspot.com/2015/01/longest-increasing-subsequence.html
    int insert(vector<int> &A, int lastIndex, int target) {
        int i = 0, j = lastIndex;
        while(i <= j) {
            int m = (i+j)/2;
            if (A[m] > target) 
               j = m - 1;
            else 
               i = m + 1;
        }
        A[i] = target;
        return i;
    }
    int longestIncreasingSubsequence(vector<int> nums) {
        int n = nums.size();
        if (n < 2) return n;
        
        vector<int> M(n, 0);
        int longest = 0;
        M[0] = nums[0];
        
        for(int i =1; i < n; i++) 
            longest = max(longest, insert(M, longest, nums[i]));
        
        return longest+1;
    }
http://www.codedisqus.com/0mSegPVkXj/longest-increasing-subsequenceonlogn.html
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