sp Archives - Huahua's Tech Road

KMP Algorithm SP19

zxi — Wed, 01 Apr 2020 03:29:45 +0000

KMP Algorithm, KMP 字符串搜索算法

Time complexity: O(m+n)
Space complexity: O(m)

Implementation

C++

#include 
#include 
using namespace std;

// Author: Huahua
namespace KMP {
vector Build(const string& p) {
  const int m = p.length();
  vector nxt{0, 0};
  for (int i = 1, j = 0; i < m; ++i) {
    while (j > 0 && p[i] != p[j])
      j = nxt[j];
    if (p[i] == p[j])
      ++j;
    nxt.push_back(j);
  }
  return nxt;
}

vector Match(const string& s, const string& p) {
  vector nxt(Build(p));
  vector ans;
  const int n = s.length();
  const int m = p.length();
  for (int i = 0, j = 0; i < n; ++i) {
    while (j > 0 && s[i] != p[j])
      j = nxt[j];
    if (s[i] == p[j])
      ++j;
    if (j == m) {
      ans.push_back(i - m + 1);
      j = nxt[j];
    }
  }
  return ans;
}
};  // namespace KMP

void CheckEQ(const vector& actual, const vector& expected) {
  if (actual != expected) {
    std::cout << "expected:";
    for (int v : expected)
      std::cout << " " << v;
    std::cout << " actual:";
    for (int v : actual)
      std::cout << " " << v;
    std::cout << std::endl;
  } else {
    std::cout << "PASS" << std::endl;
  }
}

int main(int argc, char** argv) {
  CheckEQ(KMP::Build("ABCDABD"), {0, 0, 0, 0, 0, 1, 2, 0});
  CheckEQ(KMP::Build("AB"), {0, 0, 0});
  CheckEQ(KMP::Build("A"), {0, 0});
  CheckEQ(KMP::Build("AA"), {0, 0, 1});
  CheckEQ(KMP::Build("AAA"), {0, 0, 1, 2});
  CheckEQ(KMP::Build("AABA"), {0, 0, 1, 0, 1});
  CheckEQ(KMP::Match("ABC ABCDAB ABCDABCDABDE", "ABCDABD"), {15});
  CheckEQ(KMP::Match("ABC ABCDAB ABCDABCDABDE", "AB"), {0, 4, 8, 11, 15, 19});
  CheckEQ(KMP::Match("ABC ABCDAB ABCDABCDABDE", "B"), {1, 5, 9, 12, 16, 20});
  CheckEQ(KMP::Match("AAAAA", "A"), {0, 1, 2, 3, 4});
  CheckEQ(KMP::Match("AAAAA", "AA"), {0, 1, 2, 3});
  CheckEQ(KMP::Match("AAAAA", "AAA"), {0, 1, 2});
  CheckEQ(KMP::Match("ABC", "ABC"), {0});
  return 0;
}

Python3

#!/usr/bin/env python3
from typing import List

# Author: Huahua


def Build(p: str) -> List[int]:
    m = len(p)
    nxt = [0, 0]
    j = 0
    for i in range(1, m):
        while j > 0 and p[i] != p[j]:
            j = nxt[j]
        if p[i] == p[j]:
            j += 1
        nxt.append(j)
    return nxt


def Match(s: str, p: str) -> List[int]:
    n, m = len(s), len(p)
    nxt = Build(p)
    ans = []
    j = 0
    for i in range(n):
        while j > 0 and s[i] != p[j]:
            j = nxt[j]
        if s[i] == p[j]:
            j += 1
        if j == m:
            ans.append(i - m + 1)
            j = nxt[j]
    return ans


def CheckEQ(actual, expected):
    if actual != expected:
        print('actual: %s, expected: %s' % (actual, expected))
    else:
        print('Pass')


if __name__ == "__main__":
    CheckEQ(Build("ABCDABD"), [0, 0, 0, 0, 0, 1, 2, 0])
    CheckEQ(Build("AB"), [0, 0, 0])
    CheckEQ(Build("A"), [0, 0])
    CheckEQ(Build("AA"), [0, 0, 1])
    CheckEQ(Build("AAAA"), [0, 0, 1, 2, 3])
    CheckEQ(Build("AABA"), [0, 0, 1, 0, 1])
    CheckEQ(Match("ABC ABCDAB ABCDABCDABDE", "ABCDABD"), [15])
    CheckEQ(Match("ABC ABCDAB ABCDABCDABDE", "AB"), [0, 4, 8, 11, 15, 19])
    CheckEQ(Match("ABC ABCDAB ABCDABCDABDE", "B"), [1, 5, 9, 12, 16, 20])
    CheckEQ(Match("AAAAA", "A"), [0, 1, 2, 3, 4])
    CheckEQ(Match("AAAAA", "AA"), [0, 1, 2, 3])
    CheckEQ(Match("AAAAA", "AAAA"), [0, 1])
    CheckEQ(Match("AAAAA", "AAAAA"), [0])
    CheckEQ(Match("AABAABA", "AABA"), [0, 3])

Applications

LeetCode 28. strStr()

C++

// Author: Huahua
class Solution {
public:
  int strStr(string haystack, string needle) {
    if (needle.empty()) return 0;
    auto matches = KMP::Match(haystack, needle);
    return matches.empty() ? -1 : matches[0];
  }
};

LeetCode 459. Repeated Substring Pattern

C++

// Author: Huahua
class Solution {
public:
  bool repeatedSubstringPattern(string str) {
    const int n = str.length();
    auto nxt = KMP::Build(str);
    return nxt[n] && nxt[n] % (n - nxt[n]) == 0;
  }
};

1392. Longest Happy Prefix

C++

// Author: Huahua
class Solution {
public:
  string longestPrefix(const string& s) {    
    return s.substr(0, KMP::Build(s).back());
  }
};

The post KMP Algorithm SP19 appeared first on Huahua's Tech Road.

花花酱 Binary Search II SP17

zxi — Sat, 20 Apr 2019 16:48:35 +0000

Binary Search I SP5

For the given function g(x) and a range [l, r] find the smallest int number m such that g(m) is True, if not found, return r + 1.

The post 花花酱 Binary Search II SP17 appeared first on Huahua's Tech Road.

花花酱 LeetCode Binary Trees 二叉树 SP12

zxi — Sun, 16 Dec 2018 18:24:48 +0000

Binary tree is one of the most frequently asked question type during interview.

二叉树是面试中经常会问到的问题。

The candidate needs to understand the recursively defined TreeNode and solve the problem through recursion.

面试者需要理解递归定义的TreeNode数据类型，并且通过使用递归的方式来解决问题。

The post 花花酱 LeetCode Binary Trees 二叉树 SP12 appeared first on Huahua's Tech Road.

花花酱 SP5 Binary Search

zxi — Mon, 13 Aug 2018 06:41:04 +0000

Template:

Time complexity: O(log(r-l)) * O(f(m) + g(m))

Space complexity: O(1)

"""
Returns the smallest number m such that g(m) is true.
"""
def binary_search(l, r):
  while l < r:
    m = l + (r - l) // 2
    if f(m): return m    # if m is the answer
    if g(m):
      r = m              # new range [l, m)
    else
      l = m + 1          # new range [m+1, r)
  return l               # or not found

Slides:

Lower Bound / Upper Bound

#include 
#include 
using namespace std;

int upper_bound(const vector& A, int val, int l, int r) {
  while (l < r) {
    int m = l + (r - l) / 2;
    if (A[m] > val)
      r = m;
    else      
      l = m + 1;
  }
  return l;
}

int lower_bound(const vector& A, int val, int l, int r) {
  while (l < r) {
    int m = l + (r - l) / 2;
    if (A[m] >= val)
      r = m;
    else
      l = m + 1;
  }
  return l;
}

int main() {
  vector A{1, 2, 2, 2, 4, 4, 5};
  cout << lower_bound(A, 0, 0, A.size()) << endl; // 0
  cout << lower_bound(A, 2, 0, A.size()) << endl; // 1
  cout << lower_bound(A, 3, 0, A.size()) << endl; // 4
  cout << upper_bound(A, 2, 0, A.size()) << endl; // 4
  cout << upper_bound(A, 4, 0, A.size()) << endl; // 6
  cout << upper_bound(A, 5, 0, A.size()) << endl; // 7
}

Mentioned Problems

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