53 lines
1.2 KiB
Java
53 lines
1.2 KiB
Java
package sort;
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/**
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* @author wangjunwei87
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* @since 2019-03-10
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*/
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public class KthSmallest {
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public static int kthSmallest(int[] arr, int k) {
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if (arr == null || arr.length < k) {
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return -1;
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}
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int partition = partition(arr, 0, arr.length - 1);
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while (partition + 1 != k) {
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if (partition + 1 < k) {
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partition = partition(arr, partition + 1, arr.length - 1);
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} else {
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partition = partition(arr, 0, partition - 1);
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}
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}
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return arr[partition];
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}
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private static int partition(int[] arr, int p, int r) {
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int pivot = arr[r];
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int i = p;
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for (int j = p; j < r; j++) {
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// 这里要是 <= ，不然会出现死循环，比如查找数组 [1,1,2] 的第二小的元素
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if (arr[j] <= pivot) {
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swap(arr, i, j);
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i++;
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}
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}
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swap(arr, i, r);
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return i;
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}
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private static void swap(int[] arr, int i, int j) {
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if (i == j) {
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return;
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}
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int tmp = arr[i];
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arr[i] = arr[j];
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arr[j] = tmp;
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}
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}
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