2020 年 4月 7 日「LeetCode」打卡题目：Counting Elements
Counting Elements
Given an integer array arr, count element x such that x + 1 is also in arr.
If there’re duplicates in arr, count them seperately.
Example 1:
Input: arr = [1,2,3]
Output: 2
Explanation: 1 and 2 are counted cause 2 and 3 are in arr.
Example 2:
Input: arr = [1,1,3,3,5,5,7,7]
Output: 0
Explanation: No numbers are counted, cause there's no 2, 4, 6, or 8 in arr.
Example 3:
Input: arr = [1,3,2,3,5,0]
Output: 3
Explanation: 0, 1 and 2 are counted cause 1, 2 and 3 are in arr.
Example 4:
Input: arr = [1,1,2,2]
Output: 2
Explanation: Two 1s are counted cause 2 is in arr.
Constraints:
1 <= arr.length <= 10000 <= arr[i] <= 1000
Java 代码：
public class Solution {
public int countElements(int[] arr) {
// 使用数组作为计数器，这里要多设置 2 位，坑在 count[num + 1]
int[] count = new int[1002];
for (int num : arr) {
count[num]++;
}
int res = 0;
for (int num : arr) {
if (count[num + 1] > 0) {
res += 1;
}
}
return res;
}
public static void main(String[] args) {
Solution solution = new Solution();
// int[] arr = {1, 2, 3};
// int[] arr = {1, 1, 3, 3, 5, 5, 7, 7};
// int[] arr = {1, 3, 2, 3, 5, 0};
// int[] arr = {1, 1, 2, 2};
int[] arr = {405, 220, 238, 143, 795, 820, 831, 855, 77, 402, 369, 997, 349, 185, 171, 547, 855, 80, 535, 139, 858, 988, 915, 863, 338, 927, 696, 818, 387, 834, 223, 311, 905, 589, 4, 889, 755, 678, 849, 117, 754, 460, 706, 665, 27, 484, 847, 803, 759, 152, 721, 531, 258, 215, 776, 867, 136, 104, 29, 803, 744, 972, 680, 95, 925, 107, 739, 638, 603, 373, 561, 909, 495, 573, 221, 488, 509, 109, 311, 492, 193, 513, 993, 496, 12, 625, 793, 537, 948, 957, 140, 809, 284, 93, 198, 609, 106, 12, 546, 186, 251, 827, 918, 615, 459, 999, 331, 808, 675, 164, 332, 880, 172, 134, 405, 871, 65, 155, 877, 462, 99, 84, 428, 573, 798, 273, 700, 213, 724, 826, 812, 227, 871, 556, 316, 755, 585, 911, 382, 776, 621, 936, 523, 519, 651, 441, 420, 386, 839, 739, 391, 39, 422, 992, 933, 851, 642, 503, 484, 697, 546, 444, 947, 110, 415, 737, 931, 516, 22, 741, 154, 189, 40, 568, 307, 856, 467, 887, 430, 925, 884, 914, 36, 331, 188, 78, 659, 865, 154, 133, 436, 622, 366, 699, 8, 889, 518, 386, 221, 990, 50, 719, 132, 759, 594, 908, 167, 24, 783, 843, 115, 922, 778, 813, 74, 189, 720, 832, 921, 694, 225, 367, 299, 858, 202, 67, 532, 760, 397, 171, 29, 963, 804, 511, 122, 595, 377, 34, 701, 921, 22, 456, 404, 105, 888, 646, 713, 466, 149, 154, 743, 864, 147, 571, 253, 718, 279, 471, 745, 80, 707, 239, 537, 898, 533, 451, 101, 684, 283, 261, 559, 879, 589, 932, 460, 863, 231, 980, 93, 118, 908, 762, 810, 877, 181, 719, 802, 255, 663, 698, 332, 731, 962, 177, 410, 242, 215, 526, 620, 246, 784, 842, 220, 877, 699, 972, 582, 682, 537, 797, 898, 608, 357, 326, 707, 750, 371, 950, 162, 150, 781, 254, 152, 84, 595, 60, 505, 656, 925, 546, 447, 394, 199, 595, 645, 911, 312, 335, 260, 108, 394, 724, 945, 918, 331, 577, 136, 554, 792, 231, 912, 342, 576, 172, 489, 67, 457, 468, 256, 160, 349, 238, 320, 681, 688, 293, 236, 405, 437, 370, 346, 157, 345, 225, 847, 276, 631, 129, 921, 921, 706, 20, 551, 275, 384, 426, 754, 557, 154, 339, 897, 646, 45, 632, 319, 575, 471, 553, 775, 717, 846, 782, 779, 142, 286, 644, 794, 954, 624, 320, 853, 567, 960, 39, 785, 544, 675, 337, 517, 65, 5, 470, 164, 350, 723, 446, 244, 533, 322, 970, 675, 686, 914, 185, 391, 493, 989, 713, 57, 932, 325, 491, 700, 676, 463, 346, 37, 580, 898, 246, 859, 184, 564, 229, 293, 768, 933, 614, 281, 676, 576, 438, 950, 311, 268, 582, 976, 234, 941, 496, 841, 146, 37, 279, 586, 771, 601, 92, 257, 145, 782, 164, 245, 343, 191, 877, 87, 7, 124, 801, 276, 708, 345, 647, 921, 260, 764, 475, 719, 638, 464, 507, 638, 129, 918, 803, 87, 382, 233, 75, 515, 971, 323, 228, 766, 568, 167, 942, 447, 780, 894, 401, 10, 865, 852, 583, 257, 65, 928, 681, 50, 161, 960, 890, 845, 45, 649, 128, 208, 42, 775, 789, 768, 171, 61, 932, 936, 862, 362, 553, 517, 401, 282, 173, 633, 244, 765, 37, 467, 860, 602, 301, 113, 921, 906, 104, 538, 579, 333, 259, 938, 373, 716, 918, 136, 346, 185, 934, 147, 514, 751, 9, 809, 499, 478, 13, 416, 339, 297, 911, 657, 999, 978, 534, 847, 578, 988, 574, 605, 577, 176, 449, 847, 335, 43, 494, 209, 551, 847, 508, 829, 649, 745, 428, 76, 42, 30, 407, 147, 213, 887, 56, 455, 166, 757, 911, 758, 1000, 127, 94, 583, 361, 329, 532, 350, 524, 59, 840, 854, 172, 838, 81, 300, 789, 294, 331, 898, 574, 365, 392, 6, 308, 98, 254, 324, 225, 493, 857, 494, 633, 338, 673, 131, 93, 309, 75, 436, 978, 674, 864, 8, 389, 69, 183, 545, 471, 42, 331, 923, 525, 163, 197, 954, 858, 902, 49, 377, 416, 407, 919, 983, 582, 317, 52, 544, 10, 391, 27, 221, 236, 819, 27, 478, 261, 638, 14, 519, 77, 137, 279, 570, 921, 524, 14, 813, 487, 100, 983, 961, 342, 74, 833, 732, 108, 91, 895, 727, 210, 306, 536, 9, 620, 882, 335, 84, 489, 146, 751, 379, 110, 408, 634, 958, 296, 653, 182, 987, 349, 212, 943, 305, 833, 93, 577, 842, 93, 714, 276, 5, 331, 786, 989, 195, 565, 371, 196, 187, 593, 975, 465, 379, 434, 63, 204, 360, 264, 925, 500, 67, 799, 889, 697, 655, 993, 551, 83, 42, 119, 929, 796, 817, 723, 974, 112, 190, 707, 215, 336, 499, 880, 522, 8, 246, 3, 965, 865, 646, 331, 151, 353, 225, 315, 215, 729, 431, 277, 286, 530, 141, 108, 801, 255, 800, 124, 748, 126, 477, 899, 463, 270, 591, 455, 715, 498, 233, 825, 914, 346, 602, 55, 766, 175, 784, 645, 792, 585, 105, 709, 623, 430, 360, 433, 581, 316, 86, 863, 213, 269, 600, 638, 491, 613, 61, 544, 391, 755, 322, 236, 687, 311, 344, 482, 253, 80, 780, 434, 533, 280, 930, 88, 820, 276, 583, 77, 975, 201, 658, 740, 489, 382, 746, 561, 170, 392, 565, 423, 123, 999, 665, 791, 875, 876, 873, 689, 952, 374, 424, 825, 750, 272, 243, 830, 56, 315, 608, 568, 518, 80, 760, 426, 981, 257, 503, 820, 465, 433, 885, 423, 594, 71, 254, 23, 906, 229, 993, 247, 336, 843, 755, 726, 141, 282, 260, 257, 394, 434, 786, 69, 881, 679, 269, 342, 565, 0, 966, 533, 358, 795, 525, 943, 133, 492, 593, 977, 833, 525, 338, 139, 537, 305, 482, 212, 334, 335, 534, 888, 790, 327, 261, 984, 644, 541, 987, 583, 858, 864, 340, 691, 197, 404, 995, 630, 419, 958, 593, 894, 915, 686, 380, 615};
int res = solution.countElements(arr);
System.out.println(res);
}
}