| comments | difficulty | edit_url | rating | source | tags | ||||||
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true |
中等 |
1453 |
第 192 场周赛 Q3 |
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你有一个只支持单个标签页的 浏览器 ，最开始你浏览的网页是 homepage ，你可以访问其他的网站 url ，也可以在浏览历史中后退 steps 步或前进 steps 步。
请你实现 BrowserHistory 类：
BrowserHistory(string homepage)，用homepage初始化浏览器类。void visit(string url)从当前页跳转访问url对应的页面 。执行此操作会把浏览历史前进的记录全部删除。string back(int steps)在浏览历史中后退steps步。如果你只能在浏览历史中后退至多x步且steps > x，那么你只后退x步。请返回后退 至多steps步以后的url。string forward(int steps)在浏览历史中前进steps步。如果你只能在浏览历史中前进至多x步且steps > x，那么你只前进x步。请返回前进 至多steps步以后的url。
示例：
输入：
["BrowserHistory","visit","visit","visit","back","back","forward","visit","forward","back","back"]
[["leetcode.com"],["google.com"],["facebook.com"],["youtube.com"],[1],[1],[1],["linkedin.com"],[2],[2],[7]]
输出：
[null,null,null,null,"facebook.com","google.com","facebook.com",null,"linkedin.com","google.com","leetcode.com"]
解释：
BrowserHistory browserHistory = new BrowserHistory("leetcode.com");
browserHistory.visit("google.com"); // 你原本在浏览 "leetcode.com" 。访问 "google.com"
browserHistory.visit("facebook.com"); // 你原本在浏览 "google.com" 。访问 "facebook.com"
browserHistory.visit("youtube.com"); // 你原本在浏览 "facebook.com" 。访问 "youtube.com"
browserHistory.back(1); // 你原本在浏览 "youtube.com" ，后退到 "facebook.com" 并返回 "facebook.com"
browserHistory.back(1); // 你原本在浏览 "facebook.com" ，后退到 "google.com" 并返回 "google.com"
browserHistory.forward(1); // 你原本在浏览 "google.com" ，前进到 "facebook.com" 并返回 "facebook.com"
browserHistory.visit("linkedin.com"); // 你原本在浏览 "facebook.com" 。 访问 "linkedin.com"
browserHistory.forward(2); // 你原本在浏览 "linkedin.com" ，你无法前进任何步数。
browserHistory.back(2); // 你原本在浏览 "linkedin.com" ，后退两步依次先到 "facebook.com" ，然后到 "google.com" ，并返回 "google.com"
browserHistory.back(7); // 你原本在浏览 "google.com"， 你只能后退一步到 "leetcode.com" ，并返回 "leetcode.com"
提示：
1 <= homepage.length <= 201 <= url.length <= 201 <= steps <= 100homepage和url都只包含 '.' 或者小写英文字母。- 最多调用
5000次visit，back和forward函数。
我们可以使用两个栈
调用
调用
调用
空间复杂度
class BrowserHistory:
def __init__(self, homepage: str):
self.stk1 = []
self.stk2 = []
self.visit(homepage)
def visit(self, url: str) -> None:
self.stk1.append(url)
self.stk2.clear()
def back(self, steps: int) -> str:
while steps and len(self.stk1) > 1:
self.stk2.append(self.stk1.pop())
steps -= 1
return self.stk1[-1]
def forward(self, steps: int) -> str:
while steps and self.stk2:
self.stk1.append(self.stk2.pop())
steps -= 1
return self.stk1[-1]
# Your BrowserHistory object will be instantiated and called as such:
# obj = BrowserHistory(homepage)
# obj.visit(url)
# param_2 = obj.back(steps)
# param_3 = obj.forward(steps)class BrowserHistory {
private Deque<String> stk1 = new ArrayDeque<>();
private Deque<String> stk2 = new ArrayDeque<>();
public BrowserHistory(String homepage) {
visit(homepage);
}
public void visit(String url) {
stk1.push(url);
stk2.clear();
}
public String back(int steps) {
for (; steps > 0 && stk1.size() > 1; --steps) {
stk2.push(stk1.pop());
}
return stk1.peek();
}
public String forward(int steps) {
for (; steps > 0 && !stk2.isEmpty(); --steps) {
stk1.push(stk2.pop());
}
return stk1.peek();
}
}
/**
* Your BrowserHistory object will be instantiated and called as such:
* BrowserHistory obj = new BrowserHistory(homepage);
* obj.visit(url);
* String param_2 = obj.back(steps);
* String param_3 = obj.forward(steps);
*/class BrowserHistory {
public:
stack<string> stk1;
stack<string> stk2;
BrowserHistory(string homepage) {
visit(homepage);
}
void visit(string url) {
stk1.push(url);
stk2 = stack<string>();
}
string back(int steps) {
for (; steps && stk1.size() > 1; --steps) {
stk2.push(stk1.top());
stk1.pop();
}
return stk1.top();
}
string forward(int steps) {
for (; steps && !stk2.empty(); --steps) {
stk1.push(stk2.top());
stk2.pop();
}
return stk1.top();
}
};
/**
* Your BrowserHistory object will be instantiated and called as such:
* BrowserHistory* obj = new BrowserHistory(homepage);
* obj->visit(url);
* string param_2 = obj->back(steps);
* string param_3 = obj->forward(steps);
*/type BrowserHistory struct {
stk1 []string
stk2 []string
}
func Constructor(homepage string) BrowserHistory {
t := BrowserHistory{[]string{}, []string{}}
t.Visit(homepage)
return t
}
func (this *BrowserHistory) Visit(url string) {
this.stk1 = append(this.stk1, url)
this.stk2 = []string{}
}
func (this *BrowserHistory) Back(steps int) string {
for i := 0; i < steps && len(this.stk1) > 1; i++ {
this.stk2 = append(this.stk2, this.stk1[len(this.stk1)-1])
this.stk1 = this.stk1[:len(this.stk1)-1]
}
return this.stk1[len(this.stk1)-1]
}
func (this *BrowserHistory) Forward(steps int) string {
for i := 0; i < steps && len(this.stk2) > 0; i++ {
this.stk1 = append(this.stk1, this.stk2[len(this.stk2)-1])
this.stk2 = this.stk2[:len(this.stk2)-1]
}
return this.stk1[len(this.stk1)-1]
}
/**
* Your BrowserHistory object will be instantiated and called as such:
* obj := Constructor(homepage);
* obj.Visit(url);
* param_2 := obj.Back(steps);
* param_3 := obj.Forward(steps);
*/