class Solution {
public:bool isValid(string s) {if(s.size()%2 !=0)return false;stack<char> st;for(int i=0;i<s.size();i++) {if(s[i]=='(' || s[i]=='{' || s[i]=='[')st.push(s[i]);else if(st.empty() && (s[i]=='}' || s[i]==']' || s[i]==')'))return false;else if(!st.empty()) {char ch = st.top();st.pop();if((ch=='(' && s[i]==')') || (ch=='[' && s[i]==']')||(ch=='{' && s[i]=='}'))continue;elsereturn false;}}if(!st.empty())return false;return true;}
};

class Solution {
public:string getDigits(string &s, size_t &ptr) {string ret = "";while(isdigit(s[ptr])) {ret.push_back(s[ptr++]);}return ret;}string getString(vector<string>& v){string ret;for(const auto &s : v) {ret+=s;}return ret;}string decodeString(string s) {vector<string> stk;size_t ptr = 0;while(ptr < s.size()) {char cur = s[ptr];if(isdigit(cur)) {string digits = getDigits(s,ptr);stk.push_back(digits);}else if(isalpha(cur) || cur=='[') {stk.push_back(string(1,s[ptr++]));}else{++ptr;vector<string> sub;while(stk.back()!="[") {sub.push_back(stk.back());stk.pop_back();}reverse(sub.begin(),sub.end());stk.pop_back();int repTime = stoi(stk.back());stk.pop_back();string t, o = getString(sub);while(repTime--)t+=o;stk.push_back(t);}}return getString(stk);}
};

class Solution {
public:vector<int> dailyTemperatures(vector<int>& temperatures) {if(temperatures.size()==1)return vector<int>(0);stack<int> st;vector<int> res(temperatures.size(),0);st.push(0);for(int i=0;i<temperatures.size();i++) {if(temperatures[i] <= temperatures[st.top()]) {st.push(i);}else {while(!st.empty() && temperatures[i] > temperatures[st.top()]) {res[st.top()] = i-st.top();st.pop();}st.push(i);}}return res;}
};

加粗借助一个栈min_st保存加入栈顶元素后当前栈的最小值

class MinStack {stack<int> x_st;stack<int> min_st; //辅助栈，每一个元素入栈的时候都附带存储一个当前站内元素的最小值
public:MinStack() {min_st.push(INT_MAX);}void push(int val) {x_st.push(val);min_st.push(min(min_st.top(),val));}void pop() {x_st.pop();min_st.pop();}int top() {return x_st.top();}int getMin() {return min_st.top();}
};/*** Your MinStack object will be instantiated and called as such:* MinStack* obj = new MinStack();* obj->push(val);* obj->pop();* int param_3 = obj->top();* int param_4 = obj->getMin();*/

动态规划的题

class Solution {
public:bool wordBreak(string s, vector<string>& wordDict) {unordered_set<string> wordset(wordDict.begin(),wordDict.end());vector<bool> dp(s.size()+1,false);dp[0]=true;for(int i=0;i<=s.size();i++) {for(int j=0;j<i;j++) {string str = s.substr(j,i-j);if(wordset.find(str) != wordset.end() && dp[j])dp[i]=true;}}return dp[s.size()];}
};