The Truth of Sisyphus
  • Introduction
  • Deep Learning
    • Basics
      • Hinge Loss
      • Regularizations
      • Linear Classification
      • Multi-Class and Cross Entropy Loss
      • Batch Norm and other Normalizations
      • Optimization
      • Optimization Functions
      • Convolution im2col
      • Activation Functions
      • Derivatives
        • Derivatives of Softmax
        • A Smooth (differentiable) Max Function
      • Model Ensemble
      • Layers Python Implementation
    • Classification
      • Mobile friendly networks
      • Non-local Neural Networks
      • Squeeze-and-Excitation Networks
      • Further Attention Utilization -- Efficience & Segmentation
      • Group Norm
      • ShuffleNet V2
    • Segmentation
      • Several Instance Segmentation
      • A Peek at Semantic Segmentation
      • Design Choices for Mobile Friendly Deep Learning Models, Semantic Segmentation
      • Efficient Video Object Segmentation via Network Modulation
      • BiSeNet
      • DeepLabV3+
    • Detection
      • CornerNet
      • IoU-Net
      • Why smooth L1 is popular in BBox Regression
      • MTCNN-NCNN
      • DetNet
      • SSD Illustration
    • RNN Related
      • GRU vs LSTM
      • BERT
    • Reinforcement Learning
      • AutoML in Practice Review
      • DRL for optimal execution of profolio transaction
    • Multi-task
      • Multi-task Overview
      • What are the tricks in Multi-Task network design?
    • Neural Network Interpretation
      • Neuron Visualization
    • Deep Learning Frameworks
      • How does Caffe work
      • [Gluon] When to use (Hybrid)Sequential and (Hybrid)Block
      • Gluon Hybrid Intro
      • Gluon HybridBlocks Walk-Through
      • A quick tour of Torch internals
      • NCHW / NHWC in Pytorch
      • Static & Dynamic Computation Graph
    • Converting Between DL Frameworks
      • Things To Be Considered When Doing Model Converting
      • Caffe to TensorFlow
    • Computation Graph Optimization
      • Two ways of TensorRT to optimize Neural Network Computation Graph
      • Customized Caffe Memory Optimization
      • NCNN Memory Optimization
      • Symbolic Programs Advantages: More Efficient, Reuse Intermediate Memory, Operation Folding
    • Deep Learning Debug
      • Problems caused by dead ReLU
      • Loss jumps to 87.3365
      • Common Causes of NANs During Training
    • Deployment
      • Efficient Convolution Operation
      • Quantization
    • What I read recently
      • Know Google the Paper Way
      • ECCV 2018
      • Neural Machine Translation
      • Street View OCR Extraction System
      • Teaching Machines to Draw
      • Pixel to Graph
      • Burst Image Deblurring
      • Material for Masses
      • Learning to Separate Object Sounds by Watching Unlabeled Video
    • Papers / Posts to be read
    • Dummy thoughts
  • Machine Learning
    • Classification
    • Regression
    • Clustering
    • Dimension Reduction
    • Metrics
    • Regularization
    • Bayesian Example
    • Machine Learning System Design
    • Recommendation
    • Essentials of Machine Learning
    • Linear Regression
    • Logistic Regression
      • Logistic Function
    • Gaussian Discriminant Analysis
    • Naive Bayes
    • SVM
    • MLE vs MAP
    • Boosting
    • Frequent Questions
    • Conclusion of Machine Learning
  • Python notes
    • Python _ or __ underscores usage
    • Python Multiprocess and Threading Differences
    • Heapq vs. Q.PriorityQueue
    • Python decorator
    • Understanding Python super()
    • @ property
    • Python __all__
    • Is Python List a Linked List or Array
    • What is the "u" in u'Hello world'
    • Python "self"
    • Python object and class
    • Python Class' Instance method, Class method, and Static Methods Demystified
    • Python WTF
    • Python find first value index in a list: [list].index(val)
    • Sort tuples, and lambda usecase
    • Reverse order of range()
    • Python check list is empty
    • Python get ASCII value from character
    • An A-Z of useful Python tricks
    • Python nested function variable scope
    • Python reverse a list
    • Python priority queue -- heapq
  • C++ Notes
    • Templates
    • std::string (C++) and char* (or c-string "string" for C)
    • C++ printf and cout
    • Class Member Function
    • Inline
    • Scope Resolution Operator ::
    • Constructor
    • Destructor
    • Garbage Collection is Critical
    • C++ Question Lists
  • Operating System
    • Basics
    • Mutex & Semaphore
    • Ticket Selling System
    • OS and Memory
    • Sort implementation in STL
    • Compile, link, loading & run
    • How to understand Multithreading and Multiprocessing from the view of Operating System
  • Linux & Productivity
    • Jupyter Notebook on Remote Server
    • Nividia-smi monitoring
  • Leetcode Notes
    • Array
      • 11. Container With Most Water
      • 35. Search Insert Position
    • Linked List
      • Difference between Linked List and Array
      • Linked List Insert
      • Design of Linked List
      • Two Pointers
        • 141. Linked List Cycle
        • 142. Linked List Cycle II
        • 160. Intersection of two Linked List
        • 19. Remove N-th node from the end of linked list
      • 206. Reverse Linked List
      • 203. Remove Linked List Elements
      • 328. Odd Even Linked List
      • 234. Palindrome Linked List
      • 21. Merge Two Sorted Lists
      • 430. Flatten a Multilevel Doubly Linked List
      • 430. Flatten a Multilevel Doubly Linked List
      • 708. Insert into a Cyclic Sorted List
      • 138. Copy List with Random Pointer
      • 61. Rotate List
    • Binary Tree
      • 144. Binary Tree Preorder Traversal
      • 94. Binary Tree Iterative In-order Traverse
    • Binary Search Tree
      • 98. Validate Binary Search Tree
      • 285. Inorder Successor in BST
      • 173. Binary Search Tree Iterator
      • 700. Search in a Binary Search Tree
      • 450. Delete Node in a BST
      • 701. Insert into a Binary Search Tree
      • Kth Largest Element in a Stream
      • Lowest Common Ancestor of a BST
      • Contain Duplicate III
      • Balanced BST
      • Convert Sorted Array to Binary Search Tree
    • Dynamic Programming
      • 198. House Robber
      • House Robber II
      • Unique Path
      • Unique Path II
      • Best time to buy and sell
      • Partition equal subset sum
      • Target Sum
      • Burst Ballons
    • DFS
      • Clone Graph
      • General Introduction
      • Array & String
      • Sliding Window
  • Quotes
    • Concert Violinist Joke
    • 船 Ship
    • What I cannot create, I do not understand
    • Set your course by the stars
    • To-do list
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  1. Leetcode Notes
  2. DFS

Sliding Window

Among all leetcode questions, I find that there are at least 5 substring search problem which could be solved by the sliding window algorithm. so I sum up the algorithm template here. wish it will help you!

  1. the template:

public class Solution {
    public List<Integer> slidingWindowTemplateByHarryChaoyangHe(String s, String t) {
        //init a collection or int value to save the result according the question.
        List<Integer> result = new LinkedList<>();
        if(t.length()> s.length()) return result;
        
        //create a hashmap to save the Characters of the target substring.
        //(K, V) = (Character, Frequence of the Characters)
        Map<Character, Integer> map = new HashMap<>();
        for(char c : t.toCharArray()){
            map.put(c, map.getOrDefault(c, 0) + 1);
        }
        //maintain a counter to check whether match the target string.
        int counter = map.size();//must be the map size, NOT the string size because the char may be duplicate.
        
        //Two Pointers: begin - left pointer of the window; end - right pointer of the window
        int begin = 0, end = 0;
        
        //the length of the substring which match the target string.
        int len = Integer.MAX_VALUE; 
        
        //loop at the begining of the source string
        while(end < s.length()){
            
            char c = s.charAt(end);//get a character
            
            if( map.containsKey(c) ){
                map.put(c, map.get(c)-1);// plus or minus one
                if(map.get(c) == 0) counter--;//modify the counter according the requirement(different condition).
            }
            end++;
            
            //increase begin pointer to make it invalid/valid again
            while(counter == 0 /* counter condition. different question may have different condition */){
                
                char tempc = s.charAt(begin);//***be careful here: choose the char at begin pointer, NOT the end pointer
                if(map.containsKey(tempc)){
                    map.put(tempc, map.get(tempc) + 1);//plus or minus one
                    if(map.get(tempc) > 0) counter++;//modify the counter according the requirement(different condition).
                }
                
                /* save / update(min/max) the result if find a target*/
                // result collections or result int value
                
                begin++;
            }
        }
        return result;
    }
}
  1. Firstly, here is my sliding solution this question. I will sum up the template below this code.

2) the similar questions are:

3) I will give my solution for these questions use the above template one by one

public class Solution {
    public String minWindow(String s, String t) {
        if(t.length()> s.length()) return "";
        Map<Character, Integer> map = new HashMap<>();
        for(char c : t.toCharArray()){
            map.put(c, map.getOrDefault(c,0) + 1);
        }
        int counter = map.size();
        
        int begin = 0, end = 0;
        int head = 0;
        int len = Integer.MAX_VALUE;
        
        while(end < s.length()){
            char c = s.charAt(end);
            if( map.containsKey(c) ){
                map.put(c, map.get(c)-1);
                if(map.get(c) == 0) counter--;
            }
            end++;
            
            while(counter == 0){
                char tempc = s.charAt(begin);
                if(map.containsKey(tempc)){
                    map.put(tempc, map.get(tempc) + 1);
                    if(map.get(tempc) > 0){
                        counter++;
                    }
                }
                if(end-begin < len){
                    len = end - begin;
                    head = begin;
                }
                begin++;
            }
            
        }
        if(len == Integer.MAX_VALUE) return "";
        return s.substring(head, head+len);
    }
}

you may find that I only change a little code above to solve the question "Find All Anagrams in a String": change

                if(end-begin < len){
                    len = end - begin;
                    head = begin;
                }

to

                if(end-begin == t.length()){
                    result.add(begin);
                }
public class Solution {
    public int lengthOfLongestSubstring(String s) {
        Map<Character, Integer> map = new HashMap<>();
        int begin = 0, end = 0, counter = 0, d = 0;

        while (end < s.length()) {
            // > 0 means repeating character
            //if(map[s.charAt(end++)]-- > 0) counter++;
            char c = s.charAt(end);
            map.put(c, map.getOrDefault(c, 0) + 1);
            if(map.get(c) > 1) counter++;
            end++;
            
            while (counter > 0) {
                //if (map[s.charAt(begin++)]-- > 1) counter--;
                char charTemp = s.charAt(begin);
                if (map.get(charTemp) > 1) counter--;
                map.put(charTemp, map.get(charTemp)-1);
                begin++;
            }
            d = Math.max(d, end - begin);
        }
        return d;
    }
}
public class Solution {
    public int lengthOfLongestSubstringTwoDistinct(String s) {
        Map<Character,Integer> map = new HashMap<>();
        int start = 0, end = 0, counter = 0, len = 0;
        while(end < s.length()){
            char c = s.charAt(end);
            map.put(c, map.getOrDefault(c, 0) + 1);
            if(map.get(c) == 1) counter++;//new char
            end++;
            while(counter > 2){
                char cTemp = s.charAt(start);
                map.put(cTemp, map.get(cTemp) - 1);
                if(map.get(cTemp) == 0){
                    counter--;
                }
                start++;
            }
            len = Math.max(len, end-start);
        }
        return len;
    }
}
public class Solution {
    public List<Integer> findSubstring(String S, String[] L) {
        List<Integer> res = new LinkedList<>();
        if (L.length == 0 || S.length() < L.length * L[0].length())   return res;
        int N = S.length();
        int M = L.length; // *** length
        int wl = L[0].length();
        Map<String, Integer> map = new HashMap<>(), curMap = new HashMap<>();
        for (String s : L) {
            if (map.containsKey(s))   map.put(s, map.get(s) + 1);
            else                      map.put(s, 1);
        }
        String str = null, tmp = null;
        for (int i = 0; i < wl; i++) {
            int count = 0;  // remark: reset count 
            int start = i;
            for (int r = i; r + wl <= N; r += wl) {
                str = S.substring(r, r + wl);
                if (map.containsKey(str)) {
                    if (curMap.containsKey(str))   curMap.put(str, curMap.get(str) + 1);
                    else                           curMap.put(str, 1);
                    
                    if (curMap.get(str) <= map.get(str))    count++;
                    while (curMap.get(str) > map.get(str)) {
                        tmp = S.substring(start, start + wl);
                        curMap.put(tmp, curMap.get(tmp) - 1);
                        start += wl;
                        
                        //the same as https://leetcode.com/problems/longest-substring-without-repeating-characters/
                        if (curMap.get(tmp) < map.get(tmp)) count--;
                        
                    }
                    if (count == M) {
                        res.add(start);
                        tmp = S.substring(start, start + wl);
                        curMap.put(tmp, curMap.get(tmp) - 1);
                        start += wl;
                        count--;
                    }
                }else {
                    curMap.clear();
                    count = 0;
                    start = r + wl;//not contain, so move the start
                }
            }
            curMap.clear();
        }
        return res;
    }
}
public class Solution {
    public List<Integer> findAnagrams(String s, String t) {
        List<Integer> result = new LinkedList<>();
        if(t.length()> s.length()) return result;
        Map<Character, Integer> map = new HashMap<>();
        for(char c : t.toCharArray()){
            map.put(c, map.getOrDefault(c, 0) + 1);
        }
        int counter = map.size();
        
        int begin = 0, end = 0;
        int head = 0;
        int len = Integer.MAX_VALUE;
        
        
        while(end < s.length()){
            char c = s.charAt(end);
            if( map.containsKey(c) ){
                map.put(c, map.get(c)-1);
                if(map.get(c) == 0) counter--;
            }
            end++;
            
            while(counter == 0){
                char tempc = s.charAt(begin);
                if(map.containsKey(tempc)){
                    map.put(tempc, map.get(tempc) + 1);
                    if(map.get(tempc) > 0){
                        counter++;
                    }
                }
                if(end-begin == t.length()){
                    result.add(begin);
                }
                begin++;
            }
            
        }
        return result;
    }
}
PreviousArray & StringNextQuotes

Last updated 6 years ago

Minimum-window-substring

longest substring without repeating characters

Longest Substring with At Most Two Distinct Characters

Substring with Concatenation of All Words

Find All Anagrams in a String

https://leetcode.com/problems/minimum-window-substring/
https://leetcode.com/problems/longest-substring-without-repeating-characters/
https://leetcode.com/problems/substring-with-concatenation-of-all-words/
https://leetcode.com/problems/longest-substring-with-at-most-two-distinct-characters/
https://leetcode.com/problems/find-all-anagrams-in-a-string/
https://leetcode.com/problems/minimum-window-substring/
https://leetcode.com/problems/longest-substring-without-repeating-characters/
https://leetcode.com/problems/longest-substring-with-at-most-two-distinct-characters/
https://leetcode.com/problems/substring-with-concatenation-of-all-words/
https://leetcode.com/problems/find-all-anagrams-in-a-string/