717. 1比特与2比特字符【简单题】【每日一题】
思路：
代码：
class Solution {
public boolean isOneBitCharacter(int[] bits) {
int len = bits.length,i = 0;
while (i<len){
if (bits[i] == 1){
i+=2;
}else {
if (i == len-1){
return true;
}else {
i++;
}
}
}
return false;
}
}
用时：
18. 四数之和【中等题】
思路：
代码：
直接放第4版的代码了。
class Solution {
public List<List<Integer>> fourSum(int[] nums, int target) {
List<List<Integer>> ans = new ArrayList<>();
int len = nums.length;
if (len<4){
return ans;
}
Arrays.sort(nums);
for (int i = 0; i < len-3; i++) {
if(i > 0 && nums[i] == nums[i-1]){
continue;
}
long before4_1 = (long) nums[i]+nums[i+1]+nums[i+2]+nums[i+3];
if (before4_1 > target){
break;
}else if (before4_1 == target){
ans.add(Arrays.asList(nums[i],nums[i+1],nums[i+2],nums[i+3]));
continue;
}
if ((long)nums[i]+nums[len-1]+nums[len-2]+nums[len-3] < target){
continue;
}
for (int j = i+1; j < len-2; j++) {
if(j > i+1 && nums[j] == nums[j-1]){
continue;
}
int left = j+1,right = len-1;
long pre = (long) nums[i]+nums[j],before4_2 = pre + nums[left]+nums[left+1];
if (before4_2 > target){
break;
}
if (pre +nums[right]+nums[right-1] < target){
continue;
}
while (left<right){
int cur = nums[left]+nums[right];
if (pre+cur<target){
left++;
}else if (pre+cur>target){
right--;
}else {
ans.add(Arrays.asList(nums[i],nums[j],nums[left],nums[right]));
while (left < right && nums[left] == nums[left + 1]) {
left++;
}
left++;
while (left < right && nums[right] == nums[right - 1]) {
right--;
}
right--;
}
}
}
}
return ans;
}
}
用时：
22. 括号生成【中等题】
思路：
代码：
class Solution {
public List<String> generateParenthesis(int n) {
Set<String> ans = new HashSet<>();
ans.add("()");
for (int i = 2; i <= n; i++) {
Set<String> temp = new HashSet<>();
for (String str : ans){
for (int j = 0; j < str.length(); j++) {
temp.add(str.substring(0,j)+"()"+str.substring(j));
}
}
ans = temp;
}
return new ArrayList<>(ans);
}
}
用时：
