111. Minimum Depth of Binary Tree

0111-minimum-depth-of-binary-tree/memo.md

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+### step1
+
+maximum depth of binary treeを参考に、左や右のnodeがない場合の処理だけ書いたら解けた。
+
+### step2
+
+変更点なし。
+
+### step3
+
+3回通すまで書き直し。

0111-minimum-depth-of-binary-tree/step1.cpp

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+class Solution {
+public:
+    int minDepth(TreeNode* root) {
+        if (root == nullptr) {
+            return 0;
+        }
+
+        int leftDepth = minDepth(root->left);
+        int rightDepth = minDepth(root->right);
+
+        if (leftDepth == 0) {
+            return rightDepth + 1;
+        }
+
+        if (rightDepth == 0) {
+            return leftDepth + 1;
+        }
+
+        return min(leftDepth, rightDepth) + 1;
+    }
+};

0111-minimum-depth-of-binary-tree/step2.cpp

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+class Solution {
+public:
+    int minDepth(TreeNode* root) {
+        if (root == nullptr) {
+            return 0;
+        }
+
+        int leftDepth = minDepth(root->left);
+        int rightDepth = minDepth(root->right);
+
+        if (leftDepth == 0) {
+            return rightDepth + 1;
+        }
+
+        if (rightDepth == 0) {
+            return leftDepth + 1;
+        }
+
+        return min(leftDepth, rightDepth) + 1;
+    }
+};

0111-minimum-depth-of-binary-tree/step3.cpp

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+class Solution {
+public:
+    int minDepth(TreeNode* root) {
+        if (root == nullptr) {
+            return 0;
+        }
+
+        int leftDepth = minDepth(root->left);
+        int rightDepth = minDepth(root->right);
+
+        if (leftDepth == 0) {
+            return rightDepth + 1;
+        }
+
+        if (rightDepth == 0) {
+            return leftDepth + 1;
+        }
+
+        return min(leftDepth, rightDepth) + 1;
+    }
+};