class Solution { public int specialArray(int[] nums) { Arrays.sort(nums); int n = nums.length; for (int x = 0; x <= nums[n - 1]; x++) { // 枚举 int l = 0, r = n -1 ; while (l < r) { // 二分 int m = l + r >> 1; if (nums[m] >= x) r = m; else l = m + 1; } if (nums[r] >= x && x == n - r) return x; } return -1; } }
class Solution { public: int specialArray(vector<int>& nums) { sort(nums.begin(), nums.end()); int n = nums.size(); for (int x = 0; x <= nums[n - 1]; x++) { // 枚举 int l = 0, r = n -1 ; while (l < r) { // 二分 int m = (l + r) >> 1; if (nums[m] >= x) r = m; else l = m + 1; } if (nums[r] >= x && x == n - r) return x; } return -1; } };
二分枚举+二分判定是否合法;
为了方便把判断合法单独写成函数getResgetResgetRes。
class Solution { int[] nums; public int specialArray(int[] num) { this.nums = num; Arrays.sort(nums); int l = 0, r = nums[nums.length - 1]; while (l < r) { int m = l + r >> 1; if (getRes(m) <= m) r = m; else l = m + 1; } return getRes(r) == r ? r : -1; } int getRes(int x) { int n = nums.length, l = 0, r = n - 1; while (l < r) { int m = l + r >> 1; if (nums[m] >= x) r = m; else l = m + 1; } return nums[r] >= x ? n - r : 0; } }
class Solution { public: vector<int> nums; int specialArray(vector<int>& num) { this->nums = num; sort(nums.begin(), nums.end()); int l = 0, r = nums[nums.size() - 1]; while (l < r) { int m = (l + r) >> 1; if (getRes(m) <= m) r = m; else l = m + 1; } return getRes(r) == r ? r : -1; } int getRes(int x) { int n = nums.size(), l = 0, r = n - 1; while (l < r) { int m = (l + r) >> 1; if (nums[m] >= x) r = m; else l = m + 1; } return nums[r] >= x ? n - r : 0; } };
class Solution { public int specialArray(int[] nums) { int[] cnt = new int[1001]; for (int x : nums) cnt[x]++; for (int i = 1000, tot = 0; i >= 0; i--) { tot += cnt[i]; // 数量 if (i == tot) return i; } return -1; } }
class Solution { public: int specialArray(vector<int>& nums) { int cnt[1001]; memset(cnt, 0, sizeof(cnt)); for (int x : nums) cnt[x]++; for (int i = 1000, tot = 0; i >= 0; i--) { tot += cnt[i]; if (i == tot) return i; } return -1; } };