169. 多数元素【简单】
https://leetcode-cn.com/problems/majority-element/
class Solution {
private Map<Integer, Integer> countNums(int[] nums) {
Map<Integer, Integer> counts = new HashMap<Integer, Integer>();
for (int num : nums) {
if (!counts.containsKey(num)) {
counts.put(num, 1);
} else {
counts.put(num, counts.get(num) + 1);
}
}
return counts;
}
public int majorityElement(int[] nums) {
Map<Integer, Integer> counts = countNums(nums);
Map.Entry<Integer, Integer> majorityEntry = null;
for (Map.Entry<Integer, Integer> entry : counts.entrySet()) {
if (majorityEntry == null || entry.getValue() > majorityEntry.getValue()) {
majorityEntry = entry;
}
}
return majorityEntry.getKey();
}
}
226. 翻转二叉树【简单】
https://leetcode-cn.com/problems/invert-binary-tree/
class Solution {
public TreeNode invertTree(TreeNode root) {
if (root == null || (root.left == null && root.right == null))
return root;
TreeNode left = invertTree(root.left);
TreeNode right = invertTree(root.right);
root.left = right;
root.right = left;
return root;
}
}
83. 删除排序链表中的重复元素【简单】
https://leetcode-cn.com/problems/remove-duplicates-from-sorted-list/
48. 旋转图像【中等】
https://leetcode-cn.com/problems/rotate-image/
64. 最小路径和【中等】
https://leetcode-cn.com/problems/minimum-path-sum/
