技術標籤：資料結構和演算法java

遍歷二叉樹(前序/中序/後續)
1.前序：父節點-->左子節點-->右子節點
2.中序：左子節點-->父節點-->右子節點
3.後續：左子節點-->右子節點-->父節點
注：關鍵看父節點的順序

遍歷思路:都是從根節點開始，並使用遞迴
前序：1.先返回當前節點
2.判斷左子節點是否為空，不為空則遞迴前序遍歷
3.判斷右子節點是否為空，不為空則遞迴前序遍歷
中序：1.判斷當前節點的左子節點是否為空，不為空則遞迴前序遍歷
2.返回當前節點
3.判斷右子節點是否為空，不為空則遞迴前序遍歷
後序：1.判斷當前節點的左子節點是否為空，不為空則遞迴前序遍歷

圖示

前序遍歷

中序

後序

Java程式碼

//建立二叉樹
class BinaryTree {
    private Family root;//二叉樹從根節點出發 只需要根節點

    public void setRoot(Family root) {
        this.root = root;
    }

    //前序遍歷
    public void preOrder() {
        if (this.root != null) {
            System.out.println("前序遍歷=>");
            this.root.preOrder();
        } else {
            System.out.println("樹為空");
            return;
        }
    }

    //中序遍歷
    public void midOrder() {
        if (this.root != null) {
            System.out.println("中序遍歷=>");
            this.root.midOrder();
        } else {
            System.out.println("樹為空");
            return;
        }
    }

    //後序遍歷
    public void postOrder() {
        if (this.root != null) {
            System.out.println("後序遍歷=>");
            this.root.postOrder();
        } else {
            System.out.println("樹為空");
            return;
        }
    }

    //前序查詢
    public void preFind(int no) {
        Family resFamily = this.root.preFind(no);
        if (resFamily != null) {
            System.out.printf("【no=%d,name=%s】", resFamily.getNo(), resFamily.getName());
        } else {
            System.out.println("查無此人");
        }
    }

    //中序查詢
    public void midFind(int no) {
        Family resFamily = this.root.midFind(no);
        if (resFamily != null) {
            System.out.printf("【no=%d,name=%s】", resFamily.getNo(), resFamily.getName());
        } else {
            System.out.println("查無此人");
        }
    }

    //後序查詢
    public void postFind(int no) {
        Family resFamily = this.root.postFind(no);
        if (resFamily != null) {
            System.out.printf("【no=%d,name=%s】", resFamily.getNo(), resFamily.getName());
        } else {
            System.out.println("查無此人");
        }
    }

    //刪除一個節點,樹形不能進行自刪除，如果整棵樹只有root，並且root即為目標  則整棵樹置空
    public void delFamilyByNo(int no) {
        if (this.root == null) {
            System.out.println("樹為空");
            return;
        }
        if (this.root.getNo() == no) {
            this.root = null;
            return;
        }
        this.root.delFamilyByNo(no);
    }

}

class Family {
    private int no;
    private String name;
    private Family left;//左子樹
    private Family right;//右子樹

    //初始化左右子樹預設為null
    public Family(int no, String name) {
        this.no = no;
        this.name = name;
    }

    public int getNo() {
        return no;
    }

    public void setNo(int no) {
        this.no = no;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Family getLeft() {
        return left;
    }

    public void setLeft(Family left) {
        this.left = left;
    }

    public Family getRight() {
        return right;
    }

    public void setRight(Family right) {
        this.right = right;
    }

    //前序遍歷
    public void preOrder() {
        //首先輸出根節點
        System.out.println(this);
        //遞迴遍歷左子樹
        if (this.left != null) {
            this.left.preOrder();
        }
        //遞迴遍歷右子樹
        if (this.right != null) {
            this.right.preOrder();
        }
    }

    //中序遍歷
    public void midOrder() {
        //先遞迴遍歷左子樹
        if (this.left != null) {
            this.left.midOrder();
        }
        //輸出根節點
        System.out.println(this);
        //遞迴遍歷右子樹
        if (this.right != null) {
            this.right.midOrder();
        }
    }

    //後續遍歷
    public void postOrder() {
        //遞迴遍歷左子樹
        if (this.left != null) {
            this.left.postOrder();
        }
        //遞迴遍歷右子樹
        if (this.right != null) {
            this.right.postOrder();
        }
        //輸出根節點
        System.out.println(this);

    }

    //前序查詢
    public Family preFind(int no) {
        if (this.no == no) {
            return this;
        }
        Family resFamily = null;
        if (this.left != null) {
            resFamily = this.left.preFind(no);
        }
        if (resFamily != null) {
            return resFamily;
        }
        if (this.right != null) {
            resFamily = this.right.preFind(no);
        }
        return resFamily;
    }

    //中序查詢
    public Family midFind(int no) {
        Family resFamily = null;
        if (this.left != null) {
            resFamily = this.left.preFind(no);
        }
        if (resFamily != null) {
            return resFamily;
        }
        if (this.no == no) {
            return this;
        }
        if (this.right != null) {
            resFamily = this.right.preFind(no);
        }
        return resFamily;
    }

    //後序查詢
    public Family postFind(int no) {
        Family resFamily = null;
        if (this.left != null) {
            resFamily = this.left.preFind(no);
        }
        if (resFamily != null) {
            return resFamily;
        }
        if (this.right != null) {
            resFamily = this.right.preFind(no);
        }
        if (this.no == no) {
            return this;
        }
        return resFamily;
    }

    //刪除
    //樹形不能進行自刪除，只能刪除當前節點的子節點
    public void delFamilyByNo(int no) {
        //判斷左子節點,如果滿足就把左子節點=null,並return結束遞迴
        if (this.left != null && this.left.no == no) {
            this.left = null;
            return;
        }
        //判斷右子節點，如果滿足就把右子節點=null,並return結束遞迴
        if (this.right != null && this.right.no == no) {
            this.right = null;
            return;
        }
        //遞迴左子節點刪除
        if (this.left != null) {
            this.left.delFamilyByNo(no);
        }
        //遞迴右子節點刪除
        if (this.right != null) {
            this.right.delFamilyByNo(no);
        }
    }

    @Override
    public String toString() {
        return "Family [no=" + this.no + ",name=" + this.name + "]";
    }
}