剑指offer第二天

/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public void Mirror(TreeNode root) {
        if(root != null){
            TreeNode temp = root.left;
            root.left = root.right;
            root.right = temp;
            if(root.left!=null) Mirror(root.left);
            if(root.right!=null) Mirror(root.right);
        }
    }
}

import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printMatrix(int [][] matrix) {
        if(matrix == null) return null;
        ArrayList<Integer> result = new ArrayList<>();
        int start = 0;
        while(start*2<matrix.length&&start*2<matrix[0].length){
            printMatrixCircle(matrix,start,result);
            start++;
        }
       return result;
    }
    public void printMatrixCircle(int [][] matrix,int start,ArrayList<Integer> result){
        int endX = matrix[0].length - 1 - start;
        int endY = matrix.length - 1 - start;
        for(int i = start;i <= endX;i++){
            result.add(matrix[start][i]);
        }
        if(start < endY){
            for(int i = start +1;i <= endY;i++)
                result.add(matrix[i][endX]);
        }
        if(start<endX&&start<endY)
            for(int i = endX -1;i>=start;i--)
                result.add(matrix[endY][i]);
        if(start<endX&&start<endY-1)
            for(int i = endY -1;i>start;i--)
                result.add(matrix[i][start]);
    }
}

import java.util.Stack;

public class Solution {

    Stack<Integer> stack = new Stack<Integer>();
    Stack<Integer> minStack = new Stack<Integer>();
    int min;
    public void push(int node) {
        stack.push(node);
        if(minStack.empty())
            min = node;
        else
            min = Math.min(minStack.peek(),node);
        minStack.push(min);
    }
    
    public int pop() {
        minStack.pop();
        return stack.pop();
    }
    
    public int top() {
        return stack.peek();
    }
    
    public int min() {
        return minStack.peek();
    }
}