Given two strings s and t, return true if s is a subsequence of t, or false otherwise.
A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., "ace" is a subsequence of "abcde" while "aec" is not).
Example 1:
Input: s = "abc", t = "ahbgdc" Output: true
Example 2:
Input: s = "axc", t = "ahbgdc" Output: false
Constraints:
0 <= s.length <= 1000 <= t.length <= 104sandtconsist only of lowercase English letters.
Follow up: Suppose there are lots of incoming s, say s1, s2, ..., sk where k >= 109, and you want to check one by one to see if t has its subsequence. In this scenario, how would you change your code?
/**
* @param {string} s
* @param {string} t
* @return {boolean}
*/
var isSubsequence = function(s, t) {
let current = -1
for (let i = 0; i < s.length; i++) {
const idx = t.indexOf(s[i], current + 1)
if (idx > current) {
current = idx
} else {
return false
}
}
return true
};
思路
簡單來說，通過找 s 中的字符是否在 t 中出現，並且出現的順序和 s 是否相同，來判斷 s 是否為 t 的子序列。
indexOf 的第二個變數常被忽略：
str.indexOf(searchValue[, fromIndex])
其中，str 表示要查找的字串，searchValue 表示要查找的字符或子串，fromIndex 表示查找的起始位置（選擇性）。
let str = "Hello World!";
console.log(str.indexOf("o")); // 輸出 4
console.log(str.indexOf("l", 3)); // 輸出 2
console.log(str.indexOf("x")); // 輸出 -1
