哈希表算法汇总
有效的字母异位词
leetcode.cn/problems/va…
var isAnagram = function (s, t) {
const sMap = new Map()
for (let i = 0; i < s.length; i++) {
sMap.set(s[i], sMap.get(s[i]) + 1 || 1)
}
for (let i = 0; i < t.length; i++) {
if (!sMap.has(t[i])) return false
sMap.set(t[i], sMap.get(t[i]) - 1)
if (sMap.get(t[i]) === 0) sMap.delete(t[i])
}
return sMap.size === 0
}
383. 赎金信
leetcode.cn/problems/ra…
var canConstruct = function (ransomNote, magazine) {
const mMap = new Map()
for (let i = 0; i < magazine.length; i++) {
mMap.set(magazine[i], mMap.get(magazine[i]) + 1 || 1)
}
for (let i = 0; i < ransomNote.length; i++) {
if (!mMap.has(ransomNote[i])) return false
mMap.set(ransomNote[i], mMap.get(ransomNote[i]) - 1)
if (mMap.get(ransomNote[i]) === 0) mMap.delete(ransomNote[i])
}
return true
}
49.字母异位词分组
leetcode.cn/problems/gr…
var groupAnagrams = function (strs) {
const map = new Map()
for (let i = 0; i < strs.length; i++) {
const key = strs[i].split('').sort().join('')
if (!map.has(key)) {
map.set(key, [strs[i]])
} else {
map.set(key, [...map.get(key), strs[i]])
}
}
return Array.from(map.values())
}
438. 找到字符串中所有字母异位词
leetcode.cn/problems/fi…
var findAnagrams = function (s, p) {
const res = [],
map = new Map()
let slow = 0,
fast = 0
for (let i = 0; i < p.length; i++) {
map.set(p[i], map.get(p[i]) + 1 || 1)
}
let needCnt = map.size
while (fast < s.length) {
if (map.has(s[fast])) {
map.set(s[fast], map.get(s[fast]) - 1)
}
if (map.get(s[fast]) === 0) needCnt--
slow = fast - p.length
if (map.has(s[slow])) {
map.set(s[slow], map.get(s[slow]) + 1)
if (map.get(s[slow]) === 1) needCnt++
}
if (needCnt === 0) {
res.push(slow + 1)
}
fast++
}
return res
}
349. 两个数组的交集
leetcode.cn/problems/in…
var intersection = function (nums1, nums2) {
const set = new Set()
nums1.forEach((num1) => {
if (nums2.includes(num1)) set.add(num1)
})
return Array.from(set)
}
两个数组的交集 II
leetcode.cn/problems/in…
var intersect = function (nums1, nums2) {
const res = []
for (let i = 0; i < nums1.length; i++) {
if (nums2.includes(nums1[i])) {
res.push(nums1[i])
nums2.splice(nums2.indexOf(nums1[i]), 1)
}
}
return res
}
第 202 题. 快乐数
leetcode.cn/problems/ha…
var isHappy = function (n) {
const set = new Set()
while (true) {
if (set.has(n)) return false
const sum = n
.toString()
.split('')
.reduce((pre, cur) => pre + Number(cur) ** 2, 0)
if (sum === 1) return true
set.add(n)
n = sum
}
}
两数之和
leetcode.cn/problems/tw…
var twoSum = function (nums, target) {
const map = new Map()
for (let i = 0; i < nums.length; i++) {
if (map.has(target - nums[i])) {
return [i, map.get(target - nums[i])]
}
map.set(nums[i], i)
}
}
454. 四数相加 II
leetcode.cn/problems/4s…
var fourSumCount = function (nums1, nums2, nums3, nums4) {
let res = 0
const map = new Map()
for (let i = 0; i < nums1.length; i++) {
for (let j = 0; j < nums2.length; j++) {
const sum = nums1[i] + nums2[j]
map.set(sum, map.get(sum) + 1 || 1)
}
}
for (let i = 0; i < nums3.length; i++) {
for (let j = 0; j < nums4.length; j++) {
const sum = nums3[i] + nums4[j]
if (map.has(-sum)) {
res += map.get(-sum)
}
}
}
return res
}
三数之和
leetcode.cn/problems/3s…
var threeSum = function (nums) {
nums.sort((a, b) => a - b)
const res = []
for (let i = 0; i < nums.length; i++) {
if (i !== 0 && nums[i] === nums[i - 1]) {
continue
}
if (nums[i] > 0) {
break
}
let left = i + 1,
right = nums.length - 1
while (left < right) {
const sum = nums[i] + nums[left] + nums[right]
if (sum === 0) {
res.push([nums[i], nums[left], nums[right]])
while (nums[left] === nums[left + 1]) {
left++
}
while (nums[right] === nums[right - 1]) {
right--
}
left++
right--
} else if (sum > 0) {
right--
} else {
left++
}
}
}
return res
}
四数之和
leetcode.cn/problems/4s…
var fourSum = function (nums, target) {
nums.sort((a, b) => a - b)
const res = []
for (let i = 0; i < nums.length; i++) {
if (i !== 0 && nums[i] === nums[i - 1]) continue
for (let j = i + 1; j < nums.length; j++) {
if (j !== i + 1 && nums[j] === nums[j - 1]) continue
let left = j + 1,
right = nums.length - 1
while (left < right) {
const sum = nums[i] + nums[j] + nums[left] + nums[right]
if (sum > target) {
right--
} else if (sum < target) {
left++
} else {
res.push([nums[i], nums[j], nums[left], nums[right]])
while (nums[left] === nums[left + 1]) left++
while (nums[right - 1] === nums[right]) right--
left++
right--
}
}
}
}
return res
}
