Merge pull request #1110 from xiaofei-2020/tree26

添加（0501.二叉搜索树中的众数.md）：增加typescript版本

problems/0501.二叉搜索树中的众数.md

@@ -699,6 +699,107 @@ var findMode = function(root) {
 };
 ```
 
+## TypeScript
+
+> 辅助Map法
+
+```typescript
+function findMode(root: TreeNode | null): number[] {
+    if (root === null) return [];
+    const countMap: Map<number, number> = new Map();
+    function traverse(root: TreeNode | null): void {
+        if (root === null) return;
+        countMap.set(root.val, (countMap.get(root.val) || 0) + 1);
+        traverse(root.left);
+        traverse(root.right);
+    }
+    traverse(root);
+    const countArr: number[][] = Array.from(countMap);
+    countArr.sort((a, b) => {
+        return b[1] - a[1];
+    })
+    const resArr: number[] = [];
+    const maxCount: number = countArr[0][1];
+    for (let i of countArr) {
+        if (i[1] === maxCount) resArr.push(i[0]);
+    }
+    return resArr;
+};
+```
+
+> 递归中直接解决
+
+```typescript
+function findMode(root: TreeNode | null): number[] {
+    let preNode: TreeNode | null = null;
+    let maxCount: number = 0;
+    let count: number = 0;
+    let resArr: number[] = [];
+    function traverse(root: TreeNode | null): void {
+        if (root === null) return;
+        traverse(root.left);
+        if (preNode === null) { // 第一个节点
+            count = 1;
+        } else if (preNode.val === root.val) {
+            count++;
+        } else {
+            count = 1;
+        }
+        if (count === maxCount) {
+            resArr.push(root.val);
+        } else if (count > maxCount) {
+            maxCount = count;
+            resArr.length = 0;
+            resArr.push(root.val);
+        }
+        preNode = root;
+        traverse(root.right);
+    }
+    traverse(root);
+    return resArr;
+};
+```
+
+> 迭代法
+
+```typescript
+function findMode(root: TreeNode | null): number[] {
+    const helperStack: TreeNode[] = [];
+    const resArr: number[] = [];
+    let maxCount: number = 0;
+    let count: number = 0;
+    let preNode: TreeNode | null = null;
+    let curNode: TreeNode | null = root;
+    while (curNode !== null || helperStack.length > 0) {
+        if (curNode !== null) {
+            helperStack.push(curNode);
+            curNode = curNode.left;
+        } else {
+            curNode = helperStack.pop()!;
+            if (preNode === null) { // 第一个节点
+                count = 1;
+            } else if (preNode.val === curNode.val) {
+                count++;
+            } else {
+                count = 1;
+            }
+            if (count === maxCount) {
+                resArr.push(curNode.val);
+            } else if (count > maxCount) {
+                maxCount = count;
+                resArr.length = 0;
+                resArr.push(curNode.val);
+            }
+            preNode = curNode;
+            curNode = curNode.right;
+        }
+    }
+    return resArr;
+};
+```
+
+
+
 
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