算法练习LeetCode初级算法之设计问题
-
打乱数组
不断的让第一个与后面随机选择的数交换
class Solution {
private int[] nums;
private int[] initnums;
public Solution(int[] nums) {
this.nums=nums;
this.initnums=Arrays.copyOf(nums, nums.length);//这里必须要复制，要指明对象
}
/** Resets the array to its original configuration and return it. */
public int[] reset() {
return initnums;//这里返回上面的复制
}
/** Returns a random shuffling of the array. */
public int[] shuffle() {
Random random=new Random();
for (int i = 0; i <nums.length/2; i++) {
swap(nums, 0, random.nextInt(nums.length));
}
return nums;
}
private void swap(int[] nums,int i,int j) {
int temp=nums[i];
nums[i]=nums[j];
nums[j]=temp;
}
}
-
最小栈
-
自己写的有点慢，勉强通过
class MinStack {
/** initialize your data structure here. */
Stack<Integer> stack;
public MinStack() {
stack=new Stack<>();
}
public void push(int x) {
stack.push(x);
}
public void pop() {
if (!stack.isEmpty()) {
stack.pop();
}
}
public int top() {
return stack.peek();//这里和我之前理解的不太一样，之前是取栈顶顺便就删除了
}
public int getMin() {
Stack<Integer> stack2=new Stack<>();
stack2.addAll(0, stack);
Collections.sort(stack2);
return stack2.get(0);
}
}
-
双栈法挺快
class MinStack {
/** initialize your data structure here. */
Stack<Integer> stack,minStack;
public MinStack() {
stack=new Stack<>();
minStack=new Stack<>();
}
public void push(int x) {
stack.push(x);
if (minStack.isEmpty()) {
minStack.push(x);
}else if (x<=minStack.peek()) {//此处若没有等号
minStack.push(x);
}
}
public void pop() {
if (stack.peek().equals(minStack.peek())) {//这里可能会提示栈为空的异常
stack.pop();
minStack.pop();
}else {
stack.pop();
}
}
public int top() {
return stack.peek();
}
public int getMin() {
return minStack.peek();
}
}
