# 第六周ARTS总结

# Algorithm

String to Integer (atoi) (opens new window)

3ms | 62.44% Run time
35.3MB | 99.97% Memory

public int myAtoi(String str) {
    // empty
    if (str == null || str.length() == 0 || str.trim().length() == 0) {
        return 0;
    }

    StringBuilder stringBuilder = new StringBuilder();
    for (char ch : str.trim().toCharArray()) {
        if (stringBuilder.length() == 0 && (ch == '+' || ch == '-')) {
            stringBuilder.append(ch);
            continue;
        }

        if (Character.isDigit(ch)) {
            stringBuilder.append(ch);
        } else {
            break;
        }
    }

    // if empty
    if (stringBuilder.length() == 0) {
        return 0;
    }

    // if -
    if ("-".equals(stringBuilder.toString()) || "+".equals(stringBuilder.toString())) {
        return 0;
    }

    try {
        return Integer.parseInt(stringBuilder.toString());
    } catch (NumberFormatException ex) {
        if (stringBuilder.toString().startsWith("-")) {
            return Integer.MIN_VALUE;
        } else {
            return Integer.MAX_VALUE;
        }
    }
}

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# Review

Lazy assignment in Java (opens new window)
note:While Scala and Kotlin give you the fish, Java teaches you to catch your own fish.

# Tip

断言：指明某个字符串前边或者后边将会出现满足某种规律的字符串。
想指定xxx前肯定会出现<title>，就用反向肯定预查，表达式：(?<=<title>)·*，
想指定xxx后肯定会出现</title>，就用正向肯定预查，表达式：.*(?=</title>)，
因此<title>xxx</title>通过(?<=<title>).*(?=</title>)就能匹配到xxx。

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# 第六周ARTS总结

# Algorithm

# Review

# Tip

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