二叉樹的層序遍歷算法 + 打印二叉樹所有最左邊的元素（算法）

層序遍歷

/** * 樹結構定義 */ private static class BinaryNode<T> {BinaryNode(T theElement) {this(theElement, null, null);}BinaryNode(T theElement, BinaryNode<T> lt, BinaryNode<T> rt) {element = theElement;left = lt;right = rt;}T element;BinaryNode<T> left;BinaryNode<T> right; }//層序遍歷方法 public static void levelRead(BinaryNode node) {if (node == null) {return;}//計算深度int depth = calcDepth(node);for (int i = 0; i < depth; i++) {//打印每個深度上的所有節點readLevel(node,i);}}private static void readLevel(BinaryNode node, int i) {if (node == null||i<1) {return;}//遞歸打印，如果層級為1，則打印當前節點，如果不為1，則說明還在比較高的等級，需要遞歸從頭往下繼續找當前層。if (i == 1) {System.out.print(node.element+" ");}readLevel(node.left, i-1);readLevel(node.right, i-1);}private static int calcDepth(BinaryNode node) {if (node ==null) {return 0;}int ld = calcDepth(node.left);int rd = calcDepth(node.right);if (ld>rd) {return ld+1;}else{return rd+1;} }

打印二叉樹所有最左邊的元素

在層序遍歷的基礎上，我們可以借此實現打印二叉樹上所有最左邊的元素，代碼如下：

public static void levelReadLeft(BinaryNode node) {if (node == null) {return;}int depth = calcDepth(node);for (int i = 1; i <= depth; i++) {String string = readLevelLeft(node,i);System.out.println(string);} }private static String readLevelLeft(BinaryNode node, int i) {String reString = "";if (node == null||i<1) {return reString;}if (i == 1) {return reString + (node.element+" ");}reString += readLevelLeft(node.left, i-1);if (reString.equals ("")) {reString += readLevelLeft(node.right, i-1);}return reString; }private static int calcDepth(BinaryNode node) {if (node ==null) {return 0;}int ld = calcDepth(node.left);int rd = calcDepth(node.right);if (ld>rd) {return ld+1;}else{return rd+1;} }

從頂層遍歷最右邊節點

代碼如下：

public static void levelReadRight(BinaryNode node) {if (node == null) {return;}int depth = calcDepth(node);for (int i = 1; i <= depth; i++) {String string = readLevelRight(node,i);System.out.println(string);} }private static String readLevelRight(BinaryNode node, int i) {String reString = "";if (node == null||i<1) {return reString;}if (i == 1) {return reString + (node.element+" ");}reString += readLevelRight(node.right, i-1);if (reString.equals ("")) {reString += readLevelRight(node.left, i-1);}return reString; }private static int calcDepth(BinaryNode node) {if (node ==null) {return 0;}int ld = calcDepth(node.left);int rd = calcDepth(node.right);if (ld>rd) {return ld+1;}else{return rd+1;} }

總結

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