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86 lines
2.1 KiB
86 lines
2.1 KiB
2 years ago
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package class07;
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public class Code05_IsBinarySearchTree {
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public static class TreeNode {
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public int val;
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public TreeNode left;
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public TreeNode right;
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TreeNode(int val) {
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this.val = val;
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}
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}
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public static class Info {
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public boolean isBST;
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public int max;
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public int min;
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public Info(boolean is, int ma, int mi) {
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isBST = is;
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max = ma;
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min = mi;
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}
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}
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// public static Info process(TreeNode x) {
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// if (x == null) {
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// return null;
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// }
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// Info leftInfo = process(x.left);
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// Info rightInfo = process(x.right);
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// int max = x.val;
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// int min = x.val;
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// if (leftInfo != null) {
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// max = Math.max(leftInfo.max, max);
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// min = Math.min(leftInfo.min, min);
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// }
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// if (rightInfo != null) {
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// max = Math.max(rightInfo.max, max);
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// min = Math.min(rightInfo.min, min);
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// }
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// boolean isBST = true;
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// if (leftInfo != null && !leftInfo.isBST) {
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// isBST = false;
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// }
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// if (rightInfo != null && !rightInfo.isBST) {
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// isBST = false;
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// }
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// boolean leftMaxLessX = leftInfo == null ? true : (leftInfo.max < x.val);
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// boolean rightMinMoreX = rightInfo == null ? true : (rightInfo.min > x.val);
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// if (!(leftMaxLessX && rightMinMoreX)) {
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// isBST = false;
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// }
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// return new Info(isBST, max, min);
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// }
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public static Info process(TreeNode x) {
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if (x == null) {
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return null;
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}
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Info leftInfo = process(x.left);
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Info rightInfo = process(x.right);
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int max = x.val;
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int min = x.val;
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if (leftInfo != null) {
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max = Math.max(leftInfo.max, max);
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min = Math.min(leftInfo.min, min);
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}
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if (rightInfo != null) {
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max = Math.max(rightInfo.max, max);
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min = Math.min(rightInfo.min, min);
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}
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boolean isBST = false;
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boolean leftIsBst = leftInfo == null ? true : leftInfo.isBST;
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boolean rightIsBst = rightInfo == null ? true : rightInfo.isBST;
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boolean leftMaxLessX = leftInfo == null ? true : (leftInfo.max < x.val);
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boolean rightMinMoreX = rightInfo == null ? true : (rightInfo.min > x.val);
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if (leftIsBst && rightIsBst && leftMaxLessX && rightMinMoreX) {
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isBST = true;
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}
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return new Info(isBST, max, min);
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}
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}
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