lc_模拟_0921

模拟

lc1 两数之和

class Solution {
    public int[] twoSum(int[] nums, int target) {
        HashMap<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            if (map.containsKey(target - nums[i])) {
                return new int[]{i,map.get(target-nums[i])};
            }
            map.put(nums[i], i);
        }
        return null;
    }
}

lc2 两数相加

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        int carry = 0;
        ListNode p1 = l1, p2 = l2;
        ListNode dummy = new ListNode();
        ListNode pre = dummy;
        while (p1 != null || p2 != null) {
            int num1 = p1 != null ? p1.val : 0;
            int num2 = p2 != null ? p2.val : 0;
            int num = carry + num1 + num2;
            carry = num / 10;
            pre.next = new ListNode(num % 10);
            pre = pre.next;
            if (p1 != null) {
                p1 = p1.next;
            }
            if (p2 != null) {
                p2 = p2.next;
            }
        }
        if (carry == 1) {
            pre.next = new ListNode(1);
        }
        return dummy.next;
    }
}

lc5 [最长回文子串]

//todo 留位