手痒解个iOS面试题..

题目来源请点此处

写一个方法，请将任意字符串中的"<" ">"最近的之间的内容删除，并返回其余的字符串；例如：
NSString * str1 = @"4<5";
返回 4 <5;
NSString *str2 = @"abcde";
返回 abcde;

半夜被雨吵醒..逛下发现达文哥解答了一道iOS面试题, 好久没写算法了..手痒果断来了一发..这一撸竟然就没了1个多小时..T-T..丫的, 睡觉去了..

- (NSString *)filterText:(NSString *)text {
    
    static const unichar leftBracket = '<';
    static const unichar rightBracket = '>';
    
    if (text.length > 0) {
        
        unichar *finalText = (unichar *)malloc(sizeof(unichar)*text.length);
        int i = 0;
        unichar *buffer = NULL;
        int j = 0;
        if (finalText) {
            // 是否应该缓存
            bool shouldBuffer = false;
            // 缓存开始的Index
            int startIndexOfBuffer = -1;
            // 上次遇到左括号的Index
            int lastLeftBracketIndex = 0;
            for (int k = 0; k < text.length; k++) {
                unichar _char = [text characterAtIndex:k];
                // 若遇到左括号就一直缓存字符, 直至遇到右括号才停止缓存
                if (_char == leftBracket) {
                    shouldBuffer = true;
                    if (startIndexOfBuffer < 0) {
                        startIndexOfBuffer = k;
                    }
                    lastLeftBracketIndex = k;
                    if (!buffer) {
                        buffer = (unichar *)malloc(sizeof(unichar)*(text.length-i));
                        j = 0;
                        if (!buffer) {
                            NSLog(@"开辟空间失败:[");
                            return nil;
                        }
                    }
                }
                else if (_char == rightBracket) {
                    // 遇到右括号果断关闭缓存, 可以直接写入了, 等再次遇到左括号才开启缓存
                    shouldBuffer = false;
                }
                
                if (shouldBuffer) {// 记录缓存
                    buffer[j++] = _char;
                }
                else if (!buffer) {// 不缓存则直接追加
                    finalText[i++] = _char;
                }
                else if(buffer) {// 追加缓存
                    //validCount就是要取出来的缓存字符个数, 剩下的字符抛弃(从最后一个左括号到右括号前的过滤字符)
                    int validCount = lastLeftBracketIndex-startIndexOfBuffer;
                    for (int m = 0; m < validCount; m++) {
                        finalText[i++] = buffer[m];// 丫的..这里手贱写了个m++, 找错花了好一会!!!差点怀疑人生, 挂不得输出结果老是少1个字符
                    }
                    // 重置缓存起点!
                    startIndexOfBuffer = -1;
                    free(buffer);
                    buffer = NULL;
                }
            }
        }
        else {
            NSLog(@"开辟空间失败:[");
            return nil;
        }
        NSString *fText = nil;
        // Raises an exception if characters is NULL, even if length is 0.
        if (i > 0) {
            fText = [[NSString alloc] initWithCharacters:finalText length:i];
        }
        free(finalText);
        finalText = NULL;
        
        return fText ?: @"";
    }
    return @"";
}