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Length of Last Word

描述

Given a string s consists of upper/lower-case alphabets and empty space characters ' ', return the length of last word in the string.

If the last word does not exist, return 0.

Note: A word is defined as a character sequence consists of non-space characters only.

For example, Given s = "Hello World", return 5.

分析

模拟。先从右到左找到第一个字母,然后从右到左找到第一个非字母,二者的距离就是最后一个 word 的长度。

代码

// Length of Last Word
// 偷懒,用 STL
// 时间复杂度O(n),空间复杂度O(1)
public class Solution {
public int lengthOfLastWord(String s) {
final Predicate isAlphabet = new Predicate() {
@Override
public boolean apply(char ch) {
return Character.isAlphabetic(ch);
}
};
final Predicate isNotAlphabet = new Predicate() {
@Override
public boolean apply(char ch) {
return !Character.isAlphabetic(ch);
}
};
int j = findIf(s, s.length() - 1, isAlphabet);
int i = findIf(s, j, isNotAlphabet);
return j - i;
}

interface Predicate {
boolean apply(char ch);
}
// from right to left
private static int findIf(final String s, int fromIndex, Predicate p) {
for (int i = fromIndex; i >= 0; --i) {
if (p.apply(s.charAt(i))) return i;
}
return -1;
}
}