今日学习的文章链接和视频链接
● 454.四数相加II
var fourSumCount = function(nums1, nums2, nums3, nums4) {
let count = 0
let map = new Map();
for(let number1 of nums1){
for(let number2 of nums2){
let sum = number1 + number2;
if(!map.get(sum)){
map.set(sum,1)
}else{
map.set(sum ,map.get(sum)+1)
}
}
}
for(let number1 of nums3){
for(let number2 of nums4){
let sum = number1+number2;
if(map.get(0-sum)){
count+= map.get(0-sum)
}
}
}
return count
};
● 383. 赎金信
var canConstruct = function(ransomNote, magazine) {
let map = new Map();
for(let char of magazine){
if(!map.get(char)){
map.set(char,1)
}else{
map.set(char,map.get(char)+1)
}
};
for(let char of ransomNote){
if(!map.get(char)){
return false
}else{
map.set(char,map.get(char)-1)
}
}
return true
};
● 15. 三数之和
var threeSum = function(nums) {
let res = [] ;
let len = nums.length;
nums.sort((a,b)=>a-b)
for(let i = 0 ; i < nums.length ; i++){
let l = i + 1;
let r = len-1 ;
if(nums[i]>0) return res;
if(i>0&& nums[i] == nums[i-1]){
continue;
}
while(l<r){
let sum = nums[i] + nums[l] + nums[r];
if(sum < 0 ){
l++
}else if(sum > 0 ){
r--
}else{
res.push([nums[i],nums[l],nums[r]])
while(nums[r] == nums[r-1]){
r--
}
while(nums[l] === nums[l+1]){
l++
}
r--;
l++;
}
}
}
return res
};
● 18. 四数之和
var fourSum = function (nums, target) {
if (nums.length < 4) return []
nums.sort((a, b) => a - b)
let res = []
for (let k = 0; k < nums.length - 3; k++) {
if (k > 0 && nums[k] == nums[k - 1]) continue;
for (let i = k + 1; i < nums.length - 2; i++) {
if (i > k + 1 && nums[i] == nums[i - 1]) continue;
let l = i + 1;
let r = nums.length - 1;
while (l < r) {
let sum = nums[k] + nums[i] + nums[l] + nums[r];
if (sum < target) {
l++;
continue
} else if (sum > target) {
r--;
continue
} else {
res.push([nums[k], nums[i], nums[l], nums[r]]);
while (l < r && nums[l] == nums[l + 1]) {
l++
}
while (l < r && nums[r] == nums[r - 1]) {
r--
}
l++;
r--
}
}
}
}
return res
};
今日收获，记录一下自己的学习时长
3h