又忘记带笔和本来图书馆了，只能继续复习。
复习： 163，38 (中午不到一小时) 228, 26, 27, 80(晚饭后)
LeetCode - 复习
163. Missing Ranges
又忘记int最大值的问题了
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class {
public List<String> findMissingRanges(int[] nums, int lower, int upper) {
List<String> list = new ArrayList<>();
if(nums.length == 0){
list.add(group(lower, upper));
return list;
}
if(nums[0] > lower){
list.add(group(lower, nums[0]-1));
}
for(int i = 1; i < nums.length; i++){
if(nums[i] != nums[i-1]+1 && nums[i] != nums[i-1]){
list.add(group(nums[i-1]+1, nums[i]-1));
}
}
if(nums[nums.length - 1] < upper){
list.add(group(nums[nums.length - 1]+1, upper));
}
return list;
}
private String group(int start, int end){
if(start == end){
return start + "";
}else{
return start + "->" + end;
}
}
}
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38. Count and Say
StringBuilder sb 添加 1B 要先append(1)再append(B)
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class {
public String countAndSay(int n) {
String result = "1";
for(int i=2; i <= n; i++){
StringBuilder sb = new StringBuilder();
char pre = result.charAt(0);
int num = 1;
for(int j = 1; j<result.length(); j++){
char cur = result.charAt(j);
if(cur != pre){
sb.append(num);
sb.append(pre);
pre = result.charAt(j);
num = 1;
}else{
num++;
}
}
sb.append(num);
sb.append(pre);
result = sb.toString();
}
return result;
}
}
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228. Summary Ranges
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class {
public List<String> summaryRanges(int[] nums) {
if(nums.length == 0){
return new ArrayList<>();
}
List<String> list = new ArrayList<>();
int start = 0;
for(int i=1; i < nums.length; i++){
if(nums[i] != nums[i-1] +1 && nums[i] != nums[i-1]){
list.add(group(nums[start], nums[i-1]));
start = i;
}
}
if(start < nums.length){
list.add(group(nums[start], nums[nums.length-1]));
}
return list;
}
private String group(int start, int end){
if(start == end){
return start + "";
}else{
return start + "->" + end;
}
}
}
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26. Remove Duplicates from Sorted Array
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class {
public int removeDuplicates(int[] nums) {
if(nums.length <= 1){
return nums.length;
}
int start = 0;
for(int i = 1; i < nums.length; i++){
if(nums[i] != nums[i-1]){
start++;
nums[start] = nums[i];
}
}
return start+1;
}
}
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27. Remove Element
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class {
public int removeElement(int[] nums, int val) {
if(nums.length == 0){
return 0;
}
int start = -1;
for(int i=0; i < nums.length; i++){
if(nums[i] != val){
start++;
nums[start] = nums[i];
}
}
return start+1;
}
}
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80. Remove Duplicates from Sorted Array 2
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class Solution {
public int removeDuplicates(int[] nums) {
if(nums.length < 2){
return nums.length;
}
int start = 1;
for(int i=2; i < nums.length; i++){
if(nums[i] != nums[start-1]){
start++;
nums[start] = nums[i];
}
}
return start+1;
}
}
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LeetCode - 735 (0 Easy, 1 Medium, 0 Hard)
735. Asteroid Collision - Medium
一段报错的代码
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class Solution {
public int[] asteroidCollision(int[] asteroids) {
if(asteroids.length == 0){
return new int[0];
}
Stack<Integer> stack= new Stack<>();
stack.push(asteroids[0]);
for(int i = 1; i < asteroids.length; i++){
if(asteroids[i] > 0){
stack.push(asteroids[i]);
}else{
while(asteroids[i] + stack.peek() < 0){
stack.pop();
}
if(asteroids[i] + stack.peek() == 0){
stack.pop();
}
}
}
int[] result = new int[stack.size()];
int i = 0;
for(int val : stack){
result[i++] = val;
}
return result;
}
}
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正确的代码，太多种情况了，一定要想清楚
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class Solution {
public int[] asteroidCollision(int[] a) {
if(a.length == 0){
return new int[0];
}
Stack<Integer> stack= new Stack<>();
stack.push(a[0]);
for(int i = 1; i < a.length; i++){
if(stack.isEmpty() || stack.peek()<0){
stack.push(a[i]);
}else{
if(a[i] > 0){
stack.push(a[i]);
}else{
while(!stack.isEmpty() && stack.peek() > 0 && a[i] + stack.peek() < 0){
stack.pop();
}
if(!stack.isEmpty() && a[i] + stack.peek() == 0){
stack.pop();
}else if(stack.isEmpty() || a[i] + stack.peek() < 0){
stack.push(a[i]);
}
}
}
}
int[] result = new int[stack.size()];
int i = 0;
for(int val:stack){
result[i] = val;
i++;
}
return result;
}
}
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