LeetCode 173,179

Author: LjyYano

solution/0100-0199/0173.Binary Search Tree Iterator/Solution.java

@@ -0,0 +1,52 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class BSTIterator {
+
+    Stack<TreeNode> vector = new Stack<>();
+    TreeNode current;
+
+    public BSTIterator(TreeNode root) {
+        current = root;
+        // 一直放入左儿子（左）
+        while (current != null) {
+            vector.push(current);
+            current = current.left;
+        }
+    }
+
+    /** @return whether we have a next smallest number */
+    public boolean hasNext() {
+        return !vector.isEmpty() || current != null;
+    }
+
+    /** @return the next smallest number */
+    public int next() {
+        // 一直放入左儿子（左）
+        while (current != null) {
+            vector.push(current);
+            current = current.left;
+        }
+        int ans = 0;
+        // 访问当前元素（中），把右儿子入栈（右）
+        if (!vector.isEmpty()) {
+            current = vector.pop();
+            ans = current.val;
+            current = current.right;
+        }
+        return ans;
+    }
+}
+
+/**
+ * Your BSTIterator object will be instantiated and called as such:
+ * BSTIterator obj = new BSTIterator(root);
+ * int param_1 = obj.next();
+ * boolean param_2 = obj.hasNext();
+ */

solution/0100-0199/0179.Largest Number/Solution.java

@@ -0,0 +1,23 @@
+public class Solution {
+    public String largestNumber(int[] nums) {
+
+		String[] strs = new String[nums.length];
+
+		for (int i = 0; i < strs.length; i++) {
+			strs[i] = nums[i] + "";
+		}
+
+		Arrays.sort(strs, new Comparator<String>() {
+
+			public int compare(String x, String y) {
+				return (y + x).compareTo(x + y);
+			}
+		});
+
+		if ("0".equals(strs[0])) {
+			return "0";
+		}
+
+		return String.join("", strs);
+	}
+}