434. Number of Segments in a String

434. Number of Segments in a String

Count the number of segments in a string, where a segment is defined to be a contiguous sequence of non-space characters.

Please note that the string does not contain any non-printable characters.

Example:

Input: "Hello, my name is John"
Output: 5

Key 1: Brute Force

使用两个循环, 一个跳过空格, 一个跳过非空格. 在两个循环之间判断一下, 如果尚未到达字符串末尾, 则计数加一.

class Solution {
public:
    int countSegments(string s) {
        int n = s.size(), cnt = 0, i = 0;
        while (i < n) {
            while (i < n && s[i] == ' ') ++i;
            if (i < n) ++cnt;
            while (i < n && s[i] != ' ') ++i;
        }
        return cnt;
    }
};

Key 2: Brute Force

定位每个连续非空格子串的开始点. 注意s[i] != ' ' && (i == 0 || s[i - 1] == ' ')中一定要将后两个条件用括号包围, 否则根据结合律, 表达式相当于(s[i] != ' ' && i == 0) || s[i - 1] == ' ', 是错误的.

Note: &&的优先级高于||

class Solution {
public:
    int countSegments(string s) {
        int cnt = 0;
        for (int i = 0; i < s.size(); ++i) {
            if (s[i] != ' ' && (i == 0 || s[i - 1] == ' ')) ++cnt;
        }
        return cnt;
    }
};

Key 3: stringstream

stringstream读取string时默认会跳过空格.

class Solution {
public:
    int countSegments(string s) {
        int cnt = 0;
        string word;
        stringstream ss(s);
        while (ss >> word) ++cnt;
        return cnt;
    }
};