Merge pull request wangzheng0822#77 from jerryderry/master

merge_sort and quick_sort in python

Author: wangzheng0822

python/11_sorts/sorts.py

@@ -11,8 +11,8 @@
 def bubble_sort(a: List[int]):
  if len(a) <= 1: return
 
- made_swap = False
  for i in range(len(a)):
+ made_swap = False
  for j in range(len(a) - i - 1):
  if a[j] > a[j+1]:
  a[j], a[j+1] = a[j+1], a[j]

python/12_sorts/merge_sort.py

@@ -0,0 +1,48 @@
+"""
+ Author: Wenru
+"""
+
+from typing import List
+
+def merge_sort(a: List[int]):
+ _merge_sort_between(a, 0, len(a)-1)
+
+def _merge_sort_between(a: List[int], low: int, high: int):
+ # The indices are inclusive for both low and high.
+ if low >= high: return
+ mid = low + (high - low)//2
+ _merge_sort_between(a, low, mid)
+ _merge_sort_between(a, mid+1, high)
+
+ _merge(a, low, mid, high)
+
+def _merge(a: List[int], low: int, mid: int, high: int):
+ # a[low:mid], a[mid+1, high] are sorted.
+ i, j = low, mid+1
+ tmp = []
+ while i <= mid and j <= high:
+ if a[i] <= a[j]:
+ tmp.append(a[i])
+ i += 1
+ else:
+ tmp.append(a[j])
+ j += 1
+ start = i if i <= mid else j
+ end = mid if i <= mid else high
+ tmp.extend(a[start:end+1])
+ a[low:high+1] = tmp
+
+
+if __name__ == "__main__":
+ a1 = [3, 5, 6, 7, 8]
+ a2 = [2, 2, 2, 2]
+ a3 = [4, 3, 2, 1]
+ a4 = [5, -1, 9, 3, 7, 8, 3, -2, 9]
+ merge_sort(a1)
+ print(a1)
+ merge_sort(a2)
+ print(a2)
+ merge_sort(a3)
+ print(a3)
+ merge_sort(a4)
+ print(a4)

python/12_sorts/quick_sort.py

@@ -0,0 +1,43 @@
+"""
+ Author: Wenru
+"""
+
+from typing import List
+import random
+
+def quick_sort(a: List[int]):
+ _quick_sort_between(a, 0, len(a)-1)
+
+def _quick_sort_between(a: List[int], low: int, high: int):
+ if low >= high: return
+ # get a random position as the pivot
+ k = random.randint(low, high)
+ a[low], a[k] = a[k], a[low]
+
+ m = _partition(a, low, high) # a[m] is in final position
+ _quick_sort_between(a, low, m-1)
+ _quick_sort_between(a, m+1, high)
+
+def _partition(a: List[int], low: int, high: int):
+ pivot, j = a[low], low
+ for i in range(low+1, high+1):
+ if a[i] <= pivot:
+ j += 1
+ a[j], a[i] = a[i], a[j] # swap
+ a[low], a[j] = a[j], a[low]
+ return j
+
+
+if __name__ == "__main__":
+ a1 = [3, 5, 6, 7, 8]
+ a2 = [2, 2, 2, 2]
+ a3 = [4, 3, 2, 1]
+ a4 = [5, -1, 9, 3, 7, 8, 3, -2, 9]
+ quick_sort(a1)
+ print(a1)
+ quick_sort(a2)
+ print(a2)
+ quick_sort(a3)
+ print(a3)
+ quick_sort(a4)
+ print(a4)

swift/12_sorts/.DS_Store

@@ -0,0 +1,36 @@
+//
+// QuickSort.swift
+// algo
+//
+// Created by Wenru Dong on 2018/10/17.
+// Copyright © 2018年 Wenru Dong. All rights reserved.
+//
+
+import Foundation
+
+public func quickSort<T: RandomAccessCollection & MutableCollection>(_ a: inout T) where T.Element: Comparable {
+ quickSort(&a, from: a.startIndex, to: a.index(before: a.endIndex))
+}
+
+fileprivate func quickSort<T: RandomAccessCollection & MutableCollection>(_ a: inout T, from low: T.Index, to high: T.Index) where T.Element: Comparable {
+ if low >= high { return }
+ 
+ let m = partition(&a, from: low, to: high)
+ quickSort(&a, from: low, to: a.index(before: m))
+ quickSort(&a, from: a.index(after: m), to: high)
+}
+
+fileprivate func partition<T: RandomAccessCollection & MutableCollection>(_ a: inout T, from low: T.Index, to high: T.Index) -> T.Index where T.Element: Comparable {
+ let pivot = a[low]
+ var j = low
+ var i = a.index(after: low)
+ while i <= high {
+ if a[i] < pivot {
+ a.formIndex(after: &j)
+ a.swapAt(i, j)
+ }
+ a.formIndex(after: &i)
+ }
+ a.swapAt(low, j)
+ return j
+}

swift/12_sorts/QuickSort.swift

@@ -0,0 +1,58 @@
+//
+// SortsTests.swift
+// SortsTests
+//
+// Created by Wenru Dong on 2018/10/14.
+// Copyright © 2018年 Wenru Dong. All rights reserved.
+//
+
+import XCTest
+
+class SortsTests: XCTestCase {
+ 
+ override func setUp() {
+ super.setUp()
+ // Put setup code here. This method is called before the invocation of each test method in the class.
+ }
+ 
+ override func tearDown() {
+ // Put teardown code here. This method is called after the invocation of each test method in the class.
+ super.tearDown()
+ }
+ 
+ func testMergeSort() {
+ var a1 = [1, 1, 1, 1]
+ mergeSort(&a1)
+ XCTAssertEqual(a1, [1, 1, 1, 1])
+ 
+ var a2 = [4, 3, 2, 1]
+ mergeSort(&a2)
+ XCTAssertEqual(a2, [1, 2, 3, 4])
+ 
+ var a3 = [3, 6, 9, 7, 8, -1, 9, 3, -2, 0]
+ mergeSort(&a3)
+ XCTAssertEqual(a3, [-2, -1, 0, 3, 3, 6, 7, 8, 9, 9])
+ }
+ 
+ func testQuickSort() {
+ var a1 = [1, 1, 1, 1]
+ quickSort(&a1)
+ XCTAssertEqual(a1, [1, 1, 1, 1])
+ 
+ var a2 = [4, 3, 2, 1]
+ quickSort(&a2)
+ XCTAssertEqual(a2, [1, 2, 3, 4])
+ 
+ var a3 = [3, 6, 9, 7, 8, -1, 9, 3, -2, 0]
+ quickSort(&a3)
+ XCTAssertEqual(a3, [-2, -1, 0, 3, 3, 6, 7, 8, 9, 9])
+ }
+ 
+ func testPerformanceExample() {
+ // This is an example of a performance test case.
+ self.measure {
+ // Put the code you want to measure the time of here.
+ }
+ }
+ 
+}

swift/12_sorts/SortsTests.swift

@@ -0,0 +1,52 @@
+//
+// sorts.swift
+// algo
+//
+// Created by Wenru Dong on 2018/10/14.
+// Copyright © 2018年 Wenru Dong. All rights reserved.
+//
+
+import Foundation
+
+public func mergeSort<T>(_ a: inout T) where T: RandomAccessCollection, T: MutableCollection, T.Element: Comparable {
+ mergeSort(&a, from: a.startIndex, to: a.index(before: a.endIndex))
+}
+
+fileprivate func mergeSort<T>(_ a: inout T, from low: T.Index, to high: T.Index) where T: RandomAccessCollection, T: MutableCollection, T.Element: Comparable {
+ if low >= high { return }
+ let dist = a.distance(from: low, to: high)
+ let mid = a.index(low, offsetBy: dist/2)
+ mergeSort(&a, from: low, to: mid)
+ mergeSort(&a, from: a.index(mid, offsetBy: 1), to: high)
+ merge(&a, from: low, through: mid, to: high)
+}
+
+fileprivate func merge<T>(_ a: inout T, from low: T.Index, through mid: T.Index, to high: T.Index) where T: RandomAccessCollection, T: MutableCollection, T.Element: Comparable {
+ var i = low
+ var j = a.index(mid, offsetBy: 1)
+ var tmp = Array<T.Element>()
+ tmp.reserveCapacity(a.distance(from: low, to: high) + 1)
+ while i <= mid && j <= high {
+ if a[i] <= a[j] {
+ tmp.append(a[i])
+ a.formIndex(after: &i)
+ } else {
+ tmp.append(a[j])
+ a.formIndex(after: &j)
+ }
+ }
+ 
+ var start = i
+ var end = mid
+ if j <= high {
+ start = j
+ end = high
+ }
+ tmp.append(contentsOf: a[start...end])
+ 
+ var current = low
+ for element in tmp {
+ a[current] = element
+ a.formIndex(after: &current)
+ }
+}