iOS敏感词过滤，DFA算法的OC实现

   最近给项目加个屏蔽敏感词的功能，在网上搜了一遍基本都是使用DFA算法由敏感词构造树，然后遍历输入文本，每次从树的根节点往下匹配，匹配成功则替换成*之类的即可，搜了一圈没有发现OC版的算法，故按着算法用OC写了一遍，分享一波。

   类定义如下：

#import "WordFilter.h"

#define EXIST @"isExists"

@interface WordFilter()

@property (nonatomic,strong) NSMutableDictionary *root;

@property (nonatomic,assign) BOOL isFilterClose;

@end

@implementation WordFilter

static WordFilter *instance;

+ (instancetype)sharedInstance{
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
instance = [[self alloc]init];
});
return instance;
}

   算法：

- (void)initFilter:(NSString *)filepath{

self.root = [NSMutableDictionary dictionary];
char word[1024];
FILE *fp;
char *p;

//打开文件
fp = fopen([filepath UTF8String], "r");

//按行读取内容
while (fgets(word, sizeof(word), fp)) {
p = word;

while (*p != 0) {
if (*p == '\r' || *p == '\n' || *p == ' ') {
*p = 0;
break;
}
p++;
}

//插入字符，构造节点
[self insertWords:[NSString stringWithUTF8String:word]];
}
}

-(void)insertWords:(NSString *)words{
NSMutableDictionary *node = self.root;

for (int i = 0; i < words.length; i ++) {
NSString *word = [words substringWithRange:NSMakeRange(i, 1)];

if (node[word] == nil) {
node[word] = [NSMutableDictionary dictionary];
}

node = node[word];
}

//敏感词最后一个字符标识
node[EXIST] = [NSNumber numberWithInt:1];
}

- (NSString *)filter:(NSString *)str{

if (self.isFilterClose || !self.root) {
return str;
}

NSMutableString *result = result = [str mutableCopy];

for (int i = 0; i < str.length; i ++) {
NSString *subString = [str substringFromIndex:i];
NSMutableDictionary *node = [self.root mutableCopy] ;
int num = 0;

for (int j = 0; j < subString.length; j ++) {
NSString *word = [subString substringWithRange:NSMakeRange(j, 1)];

if (node[word] == nil) {
break;
}else{
num ++;
node = node[word];
}

//敏感词匹配成功
if ([node[EXIST]integerValue] == 1) {

NSMutableString *symbolStr = [NSMutableString string];
for (int k = 0; k < num; k ++) {
[symbolStr appendString:@"*"];
}

[result replaceCharactersInRange:NSMakeRange(i, num) withString:symbolStr];

i += j;
break;
}
}
}

return result;
}

- (void)freeFilter{
self.root = nil;
}

- (void)stopFilter:(BOOL)b{
self.isFilterClose = b;
}