BM match by Objective-C

Author: Smallfly

java/17_skiplist/SkipList.java

@@ -43,19 +43,22 @@ public void insert(int value) {
       update[i] = head;
     }
 
+    // record every level largest value which smaller than insert value in update[]
     Node p = head;
     for (int i = level - 1; i >= 0; --i) {
       while (p.forwords[i] != null && p.forwords[i].data < value) {
         p = p.forwords[i];
       }
-      update[i] = p;
+      update[i] = p;// use update save node in search path
     }
 
+    // in search path node next node become new node forwords(next)
     for (int i = 0; i < level; ++i) {
       newNode.forwords[i] = update[i].forwords[i];
       update[i].forwords[i] = newNode;
     }
 
+    // update node hight
     if (levelCount < level) levelCount = level;
   }
 
@@ -78,7 +81,8 @@ public void delete(int value) {
     }
   }
 
-  private int randomLevel() {
+  // 随机 level 次，如果是奇数层数 +1，防止伪随机
+ private int randomLevel() {
     int level = 1;
     for (int i = 1; i < MAX_LEVEL; ++i) {
       if (r.nextInt() % 2 == 1) {
@@ -100,6 +104,7 @@ public void printAll() {
 
   public class Node {
     private int data = -1;
+    // 以数组形式维护下一个结点的指针
     private Node forwords[] = new Node[MAX_LEVEL];
     private int maxLevel = 0;
 

object-c/33_bm_match/BM.h

@@ -0,0 +1,19 @@
+//
+//  BM.h
+//  BM-Match
+//
+//  Created by Smallfly on 2018/12/9.
+//  Copyright © 2018 Smallfly. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface BM : NSObject
+- (instancetype)initWithA:(NSString *)a andB:(NSString *)b;
+- (NSInteger)startMatch;
+- (void)startMatchCompeletion:(void (^)(NSInteger))completion;
+@end
+
+NS_ASSUME_NONNULL_END

object-c/33_bm_match/BM.m

@@ -0,0 +1,131 @@
+//
+//  BM.m
+//  BM-Match
+//
+//  Created by Smallfly on 2018/12/9.
+//  Copyright © 2018 Smallfly. All rights reserved.
+//
+
+#import "BM.h"
+
+#define SIZE 256
+
+@interface BM()
+@property (nonatomic, strong) NSString *a; // 主串
+@property (nonatomic, strong) NSString *b; // 匹配串
+
+@property (nonatomic, strong) NSMutableArray *bc; // 匹配串，哈希表，存储字符在匹配串中的下标
+
+@property (nonatomic, strong) NSMutableArray *suffix;
+@property (nonatomic, strong) NSMutableArray *prifix;
+
+@end
+
+@implementation BM
+
+- (instancetype)initWithA:(NSString *)a andB:(NSString *)b {
+    self = [super init];
+    if (!self) return nil;
+    _a = a;
+    _b = b;
+    _bc = [NSMutableArray new];
+    _suffix = [NSMutableArray new];
+    _prifix = [NSMutableArray new];
+    [self generateBC];
+    [self generateGS];
+    return self;
+}
+
+// 构建坏字符哈希表，记录每个字符在匹配串中最后出现的位置
+- (void)generateBC {
+    for (int i = 0; i < SIZE; ++i) {
+        [_bc addObject:@-1];
+    }
+    for (int i = 0; i < _b.length; ++i) {
+        int ascii = (int)[_b characterAtIndex:i]; // char to ASCII
+        _bc[ascii] = [NSNumber numberWithInteger:i]; // save b's char index
+    }
+}
+
+- (NSInteger)bm {
+    NSInteger i = 0; // 主串和匹配串对齐的第一个字符
+    NSUInteger n = _a.length;
+    NSUInteger m = _b.length;
+    while (i <= n - m) {
+        NSInteger j;
+        // 从后往前匹配
+        for (j = m - 1; j >= 0; --j) {
+            int aValue = (int)[_a characterAtIndex:(i + j)];
+            int bValue = (int)[_b characterAtIndex:j];
+            if (aValue != bValue) break; // 找到坏字符下标 j 停止
+        }
+        if (j < 0) {
+            return i; // 匹配成功，返回所在的位置
+        }
+        
+        // 坏字符在匹配串中最后出现的位置
+        id numberInHashTableBC = _bc[(int)[_a characterAtIndex:(i + j)]];
+        NSInteger x = j - [numberInHashTableBC integerValue];
+        NSInteger y = 0;
+        if (j < m - 1) {
+            y = [self moveByGSBy:j];
+        }
+        i = i + MAX(x, y);
+        
+        // 这一步比较难理解，不直接滑到过 j，是因为在 j 之前可能存在于坏字符相同的字符
+        // 这个于坏字符相同的字符，在匹配串中的最大下标是 numberInHashTableBC
+//        i = i + (j - [numberInHashTableBC integerValue]);
+    }
+    
+    return -1;
+}
+
+// 好后缀匹配移动
+- (NSInteger)moveByGSBy:(NSInteger)j {
+    NSUInteger m = _b.length;
+    NSInteger k = m - 1 - j; // 好后缀的长度
+    NSInteger t = [_suffix[k] integerValue];
+    if (t != -1) return j - t + 1; // 匹配串的前缀，是否匹配好后缀，关键
+    for (NSInteger r = j+1; r <= m-1; ++r) {
+        if ([_prifix[m-r] boolValue]) { // 关键
+            return r;
+        }
+    }
+    return m;
+}
+
+- (void)generateGS {
+    NSUInteger m = _b.length;
+    for (NSInteger i = 0; i < m; ++i) {
+        _prifix[i] = @(NO);
+        _suffix[i] = @(-1);
+    }
+    for (NSInteger i = 0; i < m - 1; ++i) { // 从 b 中取两个字符对比
+        NSInteger j = i;
+        NSInteger k = 0; // 公共后缀的长度
+        int jValue = (int)[_b characterAtIndex:j];
+        int bmValue = (int)[_b characterAtIndex:(m-1-k)];
+        while (j >= 0 && jValue == bmValue) { // 与 b[0, m-1] 求公共子串
+            ++k;
+            --j;
+            _suffix[k] = [NSNumber numberWithInteger:(j+1)]; //j+1 代表公共子串在 b 中的起始下标
+        }
+        if (j == -1) _prifix[k] = @(YES);
+    }
+}
+
+#pragma mark -
+
+// 同步
+- (NSInteger)startMatch {
+    return [self bm];
+}
+
+// 异步
+- (void)startMatchCompeletion:(void (^)(NSInteger))completion {
+    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+        completion([self bm]);
+    });
+}
+
+@end

object-c/33_bm_match/main.m

@@ -0,0 +1,23 @@
+//
+//  main.m
+//  BM-Match
+//
+//  Created by Smallfly on 2018/12/9.
+//  Copyright © 2018 Smallfly. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+#import "BM.h"
+
+int main(int argc, const char * argv[]) {
+    @autoreleasepool {
+        BM *bm = [[BM alloc] initWithA:@"abacadc" andB:@"adc"];
+        
+        [bm startMatchCompeletion:^(NSInteger index) {
+            NSLog(@"异步查找到下标：%ld\n", index);
+        }];
+        
+        NSLog(@"同步查找到下标：%ld\n", [bm startMatch]);
+    }
+    return 0;
+}