232
- 栈的定义
stack<int> stIn; - 思路简单，用两个栈依次过滤一段数据即可实现队列效果。
class MyQueue {
public:
stack<int> stackIn;
stack<int> stackOut;
\
MyQueue() {
\
}
void push(int x) {
stackIn.push(x);
}
int pop() {
int res = -1;
if(stackOut.empty()){
while(!stackIn.empty()){
stackOut.push(stackIn.top());
stackIn.pop();
}
}
res = stackOut.top();
stackOut.pop();
return res;
}
int peek() {
int res = this->pop();
stackOut.push(res);
return res;
}
bool empty() {
if(stackIn.empty() && stackOut.empty()){
return true;
}else{
return false;
}
}
};
\
/**
* 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();
* bool param_4 = obj->empty();
*/
225
- 思路想得复杂了，用一个队列就可以实现栈。想要输出栈顶时，只需将队列的多余元素重新进队出队即可。
class MyStack {
public:
queue<int> queue;
\
MyStack() {
\
}
void push(int x) {
queue.push(x);
}
int pop() {
int size = queue.size();
while(size != 1){
int a = queue.front();
queue.pop();
queue.push(a);
size--;
}
int a = queue.front();
queue.pop();
return a;
}
int top() {
return queue.back();
}
bool empty() {
return queue.empty();
}
};
\
/**
* 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();
* bool param_4 = obj->empty();
*/
20
- 不要用if+continue， 用else if进行判断。
class Solution {
public:
bool isValid(string s) {
stack<char> stack;
if (s.size() % 2 != 0) return false;
for(int i = 0; i < s.size(); i++){
if(s[i] == '(' ){
stack.push(')');
}
else if(s[i] == '[' ){
stack.push(']');
}
else if(s[i] == '{' ){
stack.push('}');
}
else if(s[i] == ')' && !stack.empty() && stack.top() == ')'){
stack.pop();
}
else if(s[i] == ']' && !stack.empty() && stack.top() == ']'){
stack.pop();
}
else if(s[i] == '}' && !stack.empty() && stack.top() == '}'){
stack.pop();
}else{
return false;
}
}
if(stack.empty()==true){
return true;
}else{
return false;
}
}
};
1047
- 删除重复字符想到双指针，可本题要求重复删除重复字符。用栈最简单快捷。 class Solution {
public:
string removeDuplicates(string s) {
stack stack;
for(int i = 0; i < s.size(); i++ ){
if(stack.empty()){
stack.push(s[i]);
}
else if(!stack.empty() && stack.top() != s[i]){
stack.push(s[i]);
}else{
stack.pop();
}
}
string t = "";
while(!stack.empty()){
t += stack.top();
stack.pop();
}
reverse(t.begin(),t.end());
return t;
}
};
