Finding the Minimum Window in S which Contains All Elements from T | LeetCode


Related: LeetCode 67 - Minimum Window Substring
Finding the Minimum Window in S which Contains All Elements from T | LeetCode
Given a set T of characters and a string S, find the minimum window in S which will contain all the characters in T in complexity O(n).
eg,
S = “ADOBECODEBANC”
T = “ABC”
Minimum window is “BANC”.
From http://www.darrensunny.me/leetcode-minimum-window-substring/
 we can use a HashMap-like data structure (with name stat) to count the number of appearance of each character in T. Each time we encounter a character in T, we decrease its appearance in stat. We also maintain the number of matches between the characters in T and the window, by increasing it as long as the expected appearance of the encountered character is nonnegative. When the number of matches equals to the length of T, we know the current window meets the requirement.
e advance the right side of the working window if the current character is not included in T. Once it is included, we update stat and the number of matches (if necessary). And when the current window meets the requirement as we go, we advance the left side of the working window if it is safe to do, i.e. the character at the left does not appear in T, or it is redundant (observed by its expected appearance). When the left side of the window cannot be advanced, we have got a potential minimum such window.
public String minWindow(String S, String T) {
        if (S == null || S.length() == 0 || T == null || T.length() == 0)
            return "";
        int m = T.length(), n = S.length();
        // Preprocessing: count the number of appearance of each unique character in T
        HashMap<Character, Integer> stat = new HashMap<Character, Integer>();
        for (int i = 0; i < m; i++) {
            char c = T.charAt(i);
            if (stat.containsKey(c))
                stat.put(c, stat.get(c)+1);
            else
                stat.put(c, 1);
        }
        int matches = 0;        // Current number of matches
        int minimumBegin = -1, minimumEnd = n;  // Indices of the minimum window
        int begin = 0, end = 0;     // Indices of the working window
        for (; end < n; end++) {       // Move the right side of the working window
            // Move end to the next position where S[end] appears in T
            char endChar = S.charAt(end);
            if (!stat.containsKey(endChar))     // Ignore characters not in T
                continue;
            // Update stat, and matches if necessary
            stat.put(endChar, stat.get(endChar)-1); // Decrement the corresponding desired appearance
            if (stat.get(endChar) >= 0)     // The current matched character is not redundant
                matches++;
            // S[begin...end] meets the requirement
            while (matches == m) {
                // Move begin to the next position where S[begin] appears in T
                char beginChar = S.charAt(begin);
                while (!stat.containsKey(beginChar))
                    beginChar = S.charAt(++begin);
                // Update stat
                stat.put(beginChar, stat.get(beginChar)+1);
                // S[begin+1...end] lacks a character same as S[begin]
                // A possible minimum window is found
                if (stat.get(beginChar) > 0) {
                    if (end-begin < minimumEnd-minimumBegin) {
                        minimumBegin = begin;
                        minimumEnd = end;
                    }
                    matches--;
                }
                // Move the left side of the working window
                begin++;
            }
        }
        if (minimumBegin >= 0)      // A minimum such window was found
            return S.substring(minimumBegin, minimumEnd+1);
        else        // No such window was found
            return "";
    }
bool minWindow(const char* S, const char *T,
               int &minWindowBegin, int &minWindowEnd) {
  int sLen = strlen(S);
  int tLen = strlen(T);
  int needToFind[256] = {0};
  for (int i = 0; i < tLen; i++)
    needToFind[T[i]]++;
  int hasFound[256] = {0};
  int minWindowLen = INT_MAX;
  int count = 0;
  for (int begin = 0, end = 0; end < sLen; end++) {
    // skip characters not in T
    if (needToFind[S[end]] == 0) continue;
    hasFound[S[end]]++;
    if (hasFound[S[end]] <= needToFind[S[end]])
      count++;
    // if window constraint is satisfied
    if (count == tLen) {
      // advance begin index as far right as possible,
      // stop when advancing breaks window constraint.
      while (needToFind[S[begin]] == 0 ||
            hasFound[S[begin]] > needToFind[S[begin]]) {
        if (hasFound[S[begin]] > needToFind[S[begin]])
          hasFound[S[begin]]--;
        begin++;
      }
      // update minWindow if a minimum length is met
      int windowLen = end - begin + 1;
      if (windowLen < minWindowLen) {
        minWindowBegin = begin;
        minWindowEnd = end;
        minWindowLen = windowLen;
      } // end if
    } // end if
  } // end for
  return (count == tLen) ? true : false;
}

http://tech-queries.blogspot.com/2010/12/finding-minimum-window-in-array-which.html
Read full article from Finding the Minimum Window in S which Contains All Elements from T | LeetCode

Labels

LeetCode (1432) GeeksforGeeks (1122) LeetCode - Review (1067) Review (882) Algorithm (668) to-do (609) Classic Algorithm (270) Google Interview (237) Classic Interview (222) Dynamic Programming (220) DP (186) Bit Algorithms (145) POJ (141) Math (137) Tree (132) LeetCode - Phone (129) EPI (122) Cracking Coding Interview (119) DFS (115) Difficult Algorithm (115) Lintcode (115) Different Solutions (110) Smart Algorithm (104) Binary Search (96) BFS (91) HackerRank (90) Binary Tree (86) Hard (79) Two Pointers (78) Stack (76) Company-Facebook (75) BST (72) Graph Algorithm (72) Time Complexity (69) Greedy Algorithm (68) Interval (63) Company - Google (62) Geometry Algorithm (61) Interview Corner (61) LeetCode - Extended (61) Union-Find (60) Trie (58) Advanced Data Structure (56) List (56) Priority Queue (53) Codility (52) ComProGuide (50) LeetCode Hard (50) Matrix (50) Bisection (48) Segment Tree (48) Sliding Window (48) USACO (46) Space Optimization (45) Company-Airbnb (41) Greedy (41) Mathematical Algorithm (41) Tree - Post-Order (41) ACM-ICPC (40) Algorithm Interview (40) Data Structure Design (40) Graph (40) Backtracking (39) Data Structure (39) Jobdu (39) Random (39) Codeforces (38) Knapsack (38) LeetCode - DP (38) Recursive Algorithm (38) String Algorithm (38) TopCoder (38) Sort (37) Introduction to Algorithms (36) Pre-Sort (36) Beauty of Programming (35) Must Known (34) Binary Search Tree (33) Follow Up (33) prismoskills (33) Palindrome (32) Permutation (31) Array (30) Google Code Jam (30) HDU (30) Array O(N) (29) Logic Thinking (29) Monotonic Stack (29) Puzzles (29) Code - Detail (27) Company-Zenefits (27) Microsoft 100 - July (27) Queue (27) Binary Indexed Trees (26) TreeMap (26) to-do-must (26) 1point3acres (25) GeeksQuiz (25) Merge Sort (25) Reverse Thinking (25) hihocoder (25) Company - LinkedIn (24) Hash (24) High Frequency (24) Summary (24) Divide and Conquer (23) Proof (23) Game Theory (22) Topological Sort (22) Lintcode - Review (21) Tree - Modification (21) Algorithm Game (20) CareerCup (20) Company - Twitter (20) DFS + Review (20) DP - Relation (20) Brain Teaser (19) DP - Tree (19) Left and Right Array (19) O(N) (19) Sweep Line (19) UVA (19) DP - Bit Masking (18) LeetCode - Thinking (18) KMP (17) LeetCode - TODO (17) Probabilities (17) Simulation (17) String Search (17) Codercareer (16) Company-Uber (16) Iterator (16) Number (16) O(1) Space (16) Shortest Path (16) itint5 (16) DFS+Cache (15) Dijkstra (15) Euclidean GCD (15) Heap (15) LeetCode - Hard (15) Majority (15) Number Theory (15) Rolling Hash (15) Tree Traversal (15) Brute Force (14) Bucket Sort (14) DP - Knapsack (14) DP - Probability (14) Difficult (14) Fast Power Algorithm (14) Pattern (14) Prefix Sum (14) TreeSet (14) Algorithm Videos (13) Amazon Interview (13) Basic Algorithm (13) Codechef (13) Combination (13) Computational Geometry (13) DP - Digit (13) LCA (13) LeetCode - DFS (13) Linked List (13) Long Increasing Sequence(LIS) (13) Math-Divisible (13) Reservoir Sampling (13) mitbbs (13) Algorithm - How To (12) Company - Microsoft (12) DP - Interval (12) DP - Multiple Relation (12) DP - Relation Optimization (12) LeetCode - Classic (12) Level Order Traversal (12) Prime (12) Pruning (12) Reconstruct Tree (12) Thinking (12) X Sum (12) AOJ (11) Bit Mask (11) Company-Snapchat (11) DP - Space Optimization (11) Dequeue (11) Graph DFS (11) MinMax (11) Miscs (11) Princeton (11) Quick Sort (11) Stack - Tree (11) 尺取法 (11) 挑战程序设计竞赛 (11) Coin Change (10) DFS+Backtracking (10) Facebook Hacker Cup (10) Fast Slow Pointers (10) HackerRank Easy (10) Interval Tree (10) Limited Range (10) Matrix - Traverse (10) Monotone Queue (10) SPOJ (10) Starting Point (10) States (10) Stock (10) Theory (10) Tutorialhorizon (10) Kadane - Extended (9) Mathblog (9) Max-Min Flow (9) Maze (9) Median (9) O(32N) (9) Quick Select (9) Stack Overflow (9) System Design (9) Tree - Conversion (9) Use XOR (9) Book Notes (8) Company-Amazon (8) DFS+BFS (8) DP - States (8) Expression (8) Longest Common Subsequence(LCS) (8) One Pass (8) Quadtrees (8) Traversal Once (8) Trie - Suffix (8) 穷竭搜索 (8) Algorithm Problem List (7) All Sub (7) Catalan Number (7) Cycle (7) DP - Cases (7) Facebook Interview (7) Fibonacci Numbers (7) Flood fill (7) Game Nim (7) Graph BFS (7) HackerRank Difficult (7) Hackerearth (7) Inversion (7) Kadane’s Algorithm (7) Manacher (7) Morris Traversal (7) Multiple Data Structures (7) Normalized Key (7) O(XN) (7) Radix Sort (7) Recursion (7) Sampling (7) Suffix Array (7) Tech-Queries (7) Tree - Serialization (7) Tree DP (7) Trie - Bit (7) 蓝桥杯 (7) Algorithm - Brain Teaser (6) BFS - Priority Queue (6) BFS - Unusual (6) Classic Data Structure Impl (6) DP - 2D (6) DP - Monotone Queue (6) DP - Unusual (6) DP-Space Optimization (6) Dutch Flag (6) How To (6) Interviewstreet (6) Knapsack - MultiplePack (6) Local MinMax (6) MST (6) Minimum Spanning Tree (6) Number - Reach (6) Parentheses (6) Pre-Sum (6) Probability (6) Programming Pearls (6) Rabin-Karp (6) Reverse (6) Scan from right (6) Schedule (6) Stream (6) Subset Sum (6) TSP (6) Xpost (6) n00tc0d3r (6) reddit (6) AI (5) Abbreviation (5) Anagram (5) Art Of Programming-July (5) Assumption (5) Bellman Ford (5) Big Data (5) Code - Solid (5) Code Kata (5) Codility-lessons (5) Coding (5) Company - WMware (5) Convex Hull (5) Crazyforcode (5) DFS - Multiple (5) DFS+DP (5) DP - Multi-Dimension (5) DP-Multiple Relation (5) Eulerian Cycle (5) Graph - Unusual (5) Graph Cycle (5) Hash Strategy (5) Immutability (5) Java (5) LogN (5) Manhattan Distance (5) Matrix Chain Multiplication (5) N Queens (5) Pre-Sort: Index (5) Quick Partition (5) Quora (5) Randomized Algorithms (5) Resources (5) Robot (5) SPFA(Shortest Path Faster Algorithm) (5) Shuffle (5) Sieve of Eratosthenes (5) Strongly Connected Components (5) Subarray Sum (5) Sudoku (5) Suffix Tree (5) Swap (5) Threaded (5) Tree - Creation (5) Warshall Floyd (5) Word Search (5) jiuzhang (5)

Popular Posts