String
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Last updated
var myAtoi = function (str) {
const len = str.length,
max = 2 ** 31 - 1,
min = -(2 ** 31)
let ret = 0,
flag = 1,
idx = 0
while (idx < len && str[idx] === ' ') idx++
if (str[idx] === '+' || str[idx] === '-') {
flag = str[idx] === '+' ? 1 : -1
idx++
}
while (idx < len && !Number.isNaN(parseInt(str[idx], 10))) {
ret = ret * 10 + +str[idx]
idx++
}
if (ret > max || ret < min) return flag === 1 ? max : min
return flag * ret
}//纵向扫描 O(mn) - O(1)
//best version
var longestCommonPrefix = function (strs) {
if (!strs || !Array.isArray(strs) || strs.length === 0) return ''
//枚strs[0]每个char
for (let i = 0, s0Len = strs[0].length; i < s0Len; i++) {
for (let j = 1, strsLen = strs.length; j < strsLen; j++) {
//strs[j]已经到头了
if (i === strs[j].length || strs[j][i] !== strs[0][i]) {
return strs[0].substring(0, i)
}
}
}
//strs[0]都找完了
return strs[0]
}
//横向扫描 O(mn) - O(1)
var longestCommonPrefix = function (strs) {
if (!strs || !Array.isArray(strs) || strs.length === 0) return ''
let prefix = strs[0]
for (let i = 1, len = strs.length; i < len; i++) {
prefix = getLCP(prefix, strs[i])
//找不到公共前缀直接退出
if (prefix.length === 0) break
}
return prefix
function getLCP(s1, s2) {
const length = Math.min(s1.length, s2.length)
let idx = 0
while (idx < length && s1[idx] === s2[idx]) idx++
return s1.substring(0, idx)
}
}var lengthOfLastWord = function (s) {
const len = s.length
if (len === 0) return 0
let end = s.length - 1
while (end >= 0 && s[end] === ' ') end--
if (end < 0) return 0
let ret = 0
while (end >= 0 && s[end] !== ' ') {
ret++
end--
}
return ret
}//O(∣s∣) - O(∣s∣)
//loop once, filter letter and digit, then compare if target str === reverse target string
//O(∣s∣)，其中 |s| 是字符串s的长度 - O(1)
var isPalindrome = function (s) {
if (typeof s !== 'string') return false
s = s.replace(/[^A-Za-z0-9]/g, '').toLowerCase()
let l = 0,
r = s.length - 1
while (l < r) {
if (s[l++] !== s[r--]) return false
}
return true
}//使用系统函数
var reverseWords = function (s) {
return s.trim().replace(/ {2,}/g, ' ').split(' ').reverse().join(' ')
}
//use queue
var reverseWords = function (s) {
let l = 0,
r = s.length - 1,
word = ''
queue = []
while (s[l] === ' ') l++
while (s[r] === ' ') r--
//check if s still has letters
while (l <= r) {
let c = s[l]
if (c !== ' ') {
word += c
//排除单词间有多个空格的情况,否则返回如example good a
} else if (c === ' ' && word) {
queue.unshift(word)
word = ''
}
l++
}
//add last word
queue.unshift(word)
return queue.join(' ')
}//O(n+m) - O(n+m)
var compareVersion = function (version1, version2) {
const v1 = version1.split('.')
const v2 = version2.split('.')
for (let i = 0; i < v1.length || i < v2.length; i++) {
let x = 0,
y = 0
if (i < v1.length) x = parseInt(v1[i]) //parseInt已处理前导零
if (i < v2.length) y = parseInt(v2[i])
if (x > y) return 1
if (x < y) return -1
}
return 0
}
//O(n+m) - O(1)
var compareVersion = function (version1, version2) {
const len1 = version1.length,
len2 = version2.length
let i = 0,
j = 0
//任意version还没比完
while (i < len1 || j < len2) {
//比对每一段,默认是0
let x = 0
for (; i < len1 && version1[i] !== '.'; i++) {
x = x * 10 + version1[i].charCodeAt() - '0'.charCodeAt()
}
i++ // 跳过点号
let y = 0
for (; j < len2 && version2.charAt(j) !== '.'; j++) {
y = y * 10 + version2[j].charCodeAt() - '0'.charCodeAt()
}
j++ // 跳过点号
if (x !== y) return x > y ? 1 : -1
}
return 0
}//two pointer夹逼 better
var reverseString = function (s) {
let l = 0,
r = s.length - 1
while (l < r) {
;[s[l++], s[r--]] = [s[r], s[l]]
}
return s
}
//recursion
var reverseString = function (s) {
helper(s, 0, s.length - 1)
function helper(s, left, right) {
if (left >= right) return
;[s[left++], s[right--]] = [s[right], s[left]]
helper(s, left, right)
}
}//hash
var firstUniqChar = function (s) {
const obj = {}
for (let c of s) {
obj[c] ? obj[c]++ : (obj[c] = 1)
}
for (let i = 0; i < s.length; i++) {
if (obj[s[i]] === 1) return i
}
return -1
}//two pointer
var isSubsequence = function (s, t) {
let i = 0,
j = 0,
sLen = s.length,
tLen = t.length
while (i < sLen && j < tLen) {
if (s[i] === t[j]) i++
j++
}
return i === sLen
}var addStrings = function (num1, num2) {
let i = num1.length - 1,
j = num2.length - 1,
curry = 0,
ret = []
while (i >= 0 || j >= 0 || curry) {
const x = i >= 0 ? +num1[i] : 0
const y = j >= 0 ? +num2[j] : 0
const tmp = x + y + curry
ret.unshift(tmp % 10)
curry = tmp >= 10 ? 1 : 0
i--
j--
}
return ret.join('')
}var multiply = function (num1, num2) {
if (num1 === '0' || num2 === '0') {
return '0'
}
let ans = '0'
const m = num1.length,
n = num2.length
for (let i = n - 1; i >= 0; i--) {
let cur = '',
add = 0
for (let j = n - 1; j > i; j--) {
cur += 0
}
let y = num2.charAt(i) - 0
for (let j = m - 1; j >= 0; j--) {
let x = num1.charAt(j) - 0
let product = x * y + add
cur += product % 10
add = Math.floor(product / 10)
}
if (add !== 0) {
cur += add % 10
}
ans = addStrings(ans, cur.split('').reverse().join(''))
}
return ans
}
function addStrings(num1, num2) {
let i = num1.length - 1,
j = num2.length - 1,
curry = 0,
ret = []
while (i >= 0 || j >= 0 || curry) {
const x = i >= 0 ? num1.charAt(i) - 0 : 0
const y = j >= 0 ? num2.charAt(j) - 0 : 0
const tmp = x + y + curry
ret.push(tmp % 10)
curry = Math.floor(tmp / 10)
i--
j--
}
return ret.reverse().join('')
}var repeatedSubstringPattern = function (s) {
if (!s || s.length === 0) return false
let len = s.length
//子串长度不可能大于总长度的一半
for (let i = 1; i * 2 <= len; i++) {
//不超过长度一半
if (len % i === 0) {
let match = true
//依次遍历后面的
for (let j = i; j < len; j++) {
if (s[j] !== s[j - i]) {
match = false
break
}
}
if (match) return true
}
}
return false
}var reverseStr = function (s, k) {
const len = s.length
const arr = [...s]
for (let i = 0; i < len; i += 2 * k) {
reverse(arr, i, Math.min(i + k, len) - 1)
}
return arr.join('')
}
const reverse = (arr, l, r) => {
while (l < r) {
;[arr[l++], arr[r--]] = [arr[r], arr[l]]
}
}//自己写split和reverse
var reverseWords = function (s) {
function mySplit(s) {
let words = [],
word = ''
for (let i = 0; i < s.length; i++) {
if (s[i] === ' ') {
words.push(word)
word = ''
} else {
word += s[i]
}
}
words.push(word)
return words
}
function myReverse(word) {
let ret = ''
for (let i = word.length - 1; i >= 0; i--) {
ret += word[i]
}
return ret
}
let words = mySplit(s),
ret = ''
for (let word of words) {
ret += myReverse(word) + ' '
}
return ret.substring(0, ret.length - 1)
}
//使用系统函数
var reverseWords = function (s) {
let strs = s.split(' '),
ret = ''
for (let str of strs) {
ret += str.split('').reverse().join('') + ' '
}
return ret.substring(0, ret.length - 1)
}//DP
var countSubstrings = function (s) {
let len = s.length,
ret = 0
//dp[i][j] 表示字符串s在[i,j]区间的子串是否是一个回文串
let dp = Array.from({ length: len }, () => new Array(len))
//填写表格上半部分
for (let j = 0; j < len; j++) {
for (let i = 0; i <= j; i++) {
if (i === j) {
//单个字符
dp[i][j] = true
ret++
} else if (j - i === 1 && s[i] === s[j]) {
//两个相同的字符
dp[i][j] = true
ret++
} else if (j - i > 1 && s[i] === s[j] && dp[i + 1][j - 1]) {
//多于两个字符
dp[i][j] = true
ret++
}
}
}
return ret
}
//中心扩展法
var countSubstrings = function (s) {
const n = s.length
let ans = 0
for (let i = 0; i < 2 * n - 1; ++i) {
let l = i / 2,
r = i / 2 + (i % 2)
while (l >= 0 && r < n && s.charAt(l) == s.charAt(r)) {
--l
++r
++ans
}
}
return ans
}
//brute force
var countSubstrings = function (s) {
let len = s.length,
ret = 0
for (let i = 0; i < len; i++) {
for (let j = i; j < len; j++) {
if (isPalindrome(s.substring(i, j + 1))) ret++
}
}
return ret
function isPalindrome(s) {
let l = 0,
r = s.length - 1
while (l < r) {
if (s[l] !== s[r]) return false
l++
r--
}
return true
}
}var toLowerCase = function (str) {
return str.replace(/[A-Z]/g, (c)) => {
return String.fromCharCode(c.charCodeAt() + 32)
})
}//use stack O(n) - O(n)
var reverseOnlyLetters = function (S) {
const stack = []
const reg = /[a-zA-Z]/
for (let c of S) {
if (reg.test(c)) stack.push(c)
}
let ret = ''
for (let c of S) {
if (reg.test(c)) {
ret += stack.pop()
} else {
ret += c
}
}
return ret
}
//two point O(n) - O(1)
var reverseOnlyLetters = function (s) {
const len = s.length
const arr = [...s]
let l = 0,
r = len - 1
while (true) {
while (l < r && !/^[a-zA-Z]+$/.test(s[l])) l++
while (l < r && !/^[a-zA-Z]+$/.test(s[r])) r--
if (l >= r) break
;[arr[l++], arr[r--]] = [arr[r], arr[l]]
}
return arr.join('')
}//better
var replaceSpace = function (s) {
let count = 0
for (let c of s) if (c === ' ') count++
const len = s.length
const arr = new Array(len + 2 * count)
//从后往前赋值
for (let i = len - 1, j = arr.length - 1; i >= 0; i--, j--) {
if (s[i] !== ' ') {
arr[j] = s[i]
} else {
arr[j--] = '0'
arr[j--] = '2'
arr[j] = '%'
}
}
return arr.join('')
}
var replaceSpace = function (s) {
let count = 0
for (let c of s) if (c === ' ') count++
const len = s.length
const arr = new Array(len + 2 * count)
for (let i = 0, j = 0; i < len; i++) {
if (s[i] !== ' ') {
arr[j++] = s[i]
} else {
arr[j++] = '%'
arr[j++] = '2'
arr[j++] = '0'
}
}
return arr.join('')
}var reverseLeftWords = function (s, n) {
function swap(arr, l, r) {
while (l < r) {
;[arr[l++], arr[r--]] = [arr[r], arr[l]]
}
}
let arr = s.split('')
let len = arr.length
//先翻转前n个
swap(arr, 0, n - 1)
//再翻转n后面的
swap(arr, n, len - 1)
//再全翻一下
swap(arr, 0, len - 1)
return arr.join('')
}