力扣刷题篇之栈与队列篇1（待修改）
系列文章目录
目录
系列文章目录
前言
一、栈的实现
二、单调栈
总结
前言
本系列是个人力扣刷题汇总，本文是栈与队列。刷题顺序按照[力扣刷题攻略] Re：从零开始的力扣刷题生活 - 力扣（LeetCode）
一、栈的实现
两个栈实现一个队列
class MyQueue {
Stack inStack ; //输入栈
Stack outStack ;//输出栈
public MyQueue() {
inStack = new Stack<>();
outStack= new Stack<>();
}
public void push(int x) {
//往输入栈加入元素即可
inStack.push(x);
}
public int pop() {
if(outStack.isEmpty()){ //将输入栈的元素转移到输出栈
inToOut();
}
//输出栈有元素就得全部输出完，不然顺序无法得到保证
return outStack.pop();
}
public int peek() {
if(outStack.isEmpty()){ //将输入栈的元素转移到输出栈
inToOut();
}
return outStack.peek();
}
public boolean empty() {
return inStack.isEmpty()&&outStack.isEmpty();
}
//将输入栈的元素转移到输出栈
public void inToOut(){
while(!inStack.isEmpty()){
outStack.push(inStack.pop());
}
}
}
/**
* Your MyQueue object will be instantiated and called as such:
* MyQueue obj = new MyQueue();
* obj.push(x);
* int param_2 = obj.pop();
* int param_3 = obj.peek();
* boolean param_4 = obj.empty();
*/ 
两个队列来实现一个栈
class MyStack {
private Queue a;//输入队列
private Queue b;//输出队列
public MyStack() {
a = new LinkedList<>();
b = new LinkedList<>();
}
public void push(int x) {
a.offer(x);
// 将b队列中元素全部转给a队列
while(!b.isEmpty())
a.offer(b.poll());
// 交换a和b,使得a队列没有在push()的时候始终为空队列
Queue temp = a;
a = b;
b = temp;
}
public int pop() {
return b.poll();
}
public int top() {
return b.peek();
}
public boolean empty() {
return b.isEmpty();
}
}
/**
* Your MyStack object will be instantiated and called as such:
* MyStack obj = new MyStack();
* obj.push(x);
* int param_2 = obj.pop();
* int param_3 = obj.top();
* boolean param_4 = obj.empty();
*/ 
这题看不懂
class TripleInOne {
private int stackSize;
private int[] index;
private int[][] stack;
public TripleInOne(int stackSize) {
this.stackSize=stackSize;
this.index=new int[]{-1,-1,-1};
this.stack=new int[3][stackSize];
}
public void push(int stackNum, int value) {
if(index[stackNum]+1
class Solution {
public List buildArray(int[] target, int n) {
List res = new ArrayList<>();
int idx = 1;
for (int i = 0; i < target.length; ++i) {
int cur = target[i];
while (cur > idx) {
res.add("Push"); res.add("Pop");
idx++;
}
res.add("Push");
idx++;
}
return res;
}
} 
二、单调栈
class Solution {
public int[] nextGreaterElement(int[] nums1, int[] nums2) {
int M = nums1.length;
int N = nums2.length;
int[] answer = new int[M];
// 使用数组代替map
int[] map = new int[10001];
for (int i = 0; i < M; i++) {
map[nums1[i]] = i + 1;
}
int[] stack = new int[N];
int size = 0;
// 逆序寻找
for (int i = N - 1; i >=0; i--) {
// 弹出栈顶比当前元素小的数
while (size > 0 && stack[size - 1] < nums2[i]){
size--;
}
// map中含有的才计算
if(map[nums2[i]] != 0){
answer[map[nums2[i]] - 1] = size == 0 ? -1 : stack[size - 1];
}
stack[size++] = nums2[i];
}
return answer;
}
}
class Solution {
public int largestRectangleArea(int[] heights) {
int n = heights.length;
int[] stack = new int[n + 1];
int top = 0;
int res = 0;
for (int i = 0; i < n; i++) {
while (top > 0 && heights[i] <= heights[stack[top]]) {
int temp = stack[top--];
res = Math.max(res, (i - (top == 0 ? -1 : stack[top]) - 1) * heights[temp]);
}
stack[++top] = i;
}
while (top > 0) {
int temp = stack[top--];
res = Math.max(res, (n - (top == 0 ? -1 : stack[top]) - 1) * heights[temp]);
}
return res;
}
}
class Solution {
public int[] dailyTemperatures(int[] temperatures) {
int n = temperatures.length;
int[] dp = new int[n];
dp[n - 1] = 0;
for (int i = n - 2; i >= 0; i--) {
if (temperatures[i] < temperatures[i + 1]) {
dp[i] = 1;
} else {
int t = i + 1;
while (t < n) {
if (temperatures[i] < temperatures[t]) {
dp[i] = t - i;
break;
}
if (dp[t] == 0){
break;
}
t = t + dp[t];
}
}
}
return dp;
}
}
// class StockSpanner {
// List> nums;
// public StockSpanner() {
// nums = new ArrayList<>();
// }
// public int next(int price) {
// int n = nums.size(), i = n - 1;
// while (i >= 0 && price >= nums.get(i).getKey()) {
// i -= nums.get(i).getValue();
// }
// nums.add(new Pair(price, n - i));
// return n - i;
// }
// }
// /**
// * Your StockSpanner object will be instantiated and called as such:
// * StockSpanner obj = new StockSpanner();
// * int param_1 = obj.next(price);
// */
// class StockSpanner {
// Deque stack;
// int idx;
// public StockSpanner() {
// stack = new ArrayDeque();
// stack.push(new int[]{-1, Integer.MAX_VALUE});
// idx = -1;
// }
// public int next(int price) {
// idx ++;
// while(price >= stack.peek()[1]) {
// stack.pop();
// }
// int res = idx - stack.peek()[0];
// stack.push(new int[]{idx, price});
// return res;
// }
// }
// /**
// * Your StockSpanner object will be instantiated and called as such:
// * StockSpanner obj = new StockSpanner();
// * int param_1 = obj.next(price);
// */
class StockSpanner {
Deque stack;
int idx;
public StockSpanner() {
stack = new ArrayDeque();
stack.push(new int[]{-1, Integer.MAX_VALUE});
idx = -1;
}
public int next(int price) {
idx ++;
while(price >= stack.peek()[1]) {
stack.pop();
}
int res = idx - stack.peek()[0];
stack.push(new int[]{idx, price});
return res;
}
}
/**
* Your StockSpanner object will be instantiated and called as such:
* StockSpanner obj = new StockSpanner();
* int param_1 = obj.next(price);
*/ 
class Solution {
public int trap(int[] height) {
// int n = height.length;
// // left[i]表示i左边的最大值，right[i]表示i右边的最大值
// int[] left=new int[n];
// int[] right=new int[n];
// for (int i = 1; i < n; i++) {
// left[i] = Math.max(left[i - 1], height[i - 1]);
// }
// for (int i = n - 2; i >= 0; i--) {
// right[i] = Math.max(right[i + 1], height[i + 1]);
// }
// int water = 0;
// for (int i = 1; i < n; i++) {
// int level = Math.min(left[i], right[i]);
// water += Math.max(0, level - height[i]);
// }
// return water;
int sum = 0;
int max_left = 0;
int max_right = 0;
int left = 1;
int right = height.length - 2; // 加右指针进去
for (int i = 1; i < height.length - 1; i++) {
//从左到右更
if (height[left - 1] < height[right + 1]) {
max_left = Math.max(max_left, height[left - 1]);
// int min = max_left;
if (max_left > height[left]) {
sum = sum + (max_left - height[left]);
}
left++;
//从右到左更
} else {
max_right = Math.max(max_right, height[right + 1]);
// int min = max_right;
if (max_right > height[right]) {
sum = sum + (max_right - height[right]);
}
right--;
}
}
return sum;
}
}总结
sorry，这几天我估计要降低下更新频率了。
