Commit 502d663

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Add max heap approach for No.215

Signed-off-by: begeekmyfriend <begeekmyfriend@gmail.com>

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0215_kth_largest_element_in_an_array
- kth_elem.c

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`‎0215_kth_largest_element_in_an_array/kth_elem.c‎`

Lines changed: 44 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -1,13 +1,43 @@`
`1`	`1`	`#include <stdio.h>`
`2`	`2`	`#include <stdlib.h>`
`3`	`3`
	`4`	`+`
`4`	`5`	`static inline void swap(int a, int b)`
`5`	`6`	`{`
`6`	`7`	`int t = *a;`
`7`	`8`	`a = b;`
`8`	`9`	`*b = t;`
`9`	`10`	`}`
`10`	`11`
	`12`	`+static void max_heapify(int *nums, int size, int parent)`
	`13`	`+{`
	`14`	`+ int i = parent; /* parent is the root */`
	`15`	`+ int l = parent * 2 + 1;`
	`16`	`+ int r = parent * 2 + 2;`
	`17`	`+`
	`18`	`+ if (l < size && nums[l] > nums[i]) {`
	`19`	`+ i = l;`
	`20`	`+ }`
	`21`	`+`
	`22`	`+ if (r < size && nums[r] > nums[i]) {`
	`23`	`+ i = r;`
	`24`	`+ }`
	`25`	`+`
	`26`	`+ /* percolate up */`
	`27`	`+ if (i != parent) {`
	`28`	`+ swap(&nums[i], &nums[parent]);`
	`29`	`+ max_heapify(nums, size, i);`
	`30`	`+ }`
	`31`	`+}`
	`32`	`+`
	`33`	`+static void build_max_heap(int *nums, int size)`
	`34`	`+{`
	`35`	`+ int i;`
	`36`	`+ for (i = size / 2; i >= 0; i--) {`
	`37`	`+ max_heapify(nums, size, i);`
	`38`	`+ }`
	`39`	`+}`
	`40`	`+`
`11`	`41`	`static int quick_select(int *nums, int lo, int hi, int k)`
`12`	`42`	`{`
`13`	`43`	`if (lo >= hi) {`
`@@ -40,8 +70,22 @@ static int quick_select(int *nums, int lo, int hi, int k)`
`40`	`70`
`41`	`71`	`int findKthLargest(int* nums, int numsSize, int k)`
`42`	`72`	`{`
	`73`	`+#if 0`
`43`	`74`	`int i = quick_select(nums, 0, numsSize - 1, k);`
`44`	`75`	`return nums[i];`
	`76`	`+#else`
	`77`	`+ int i;`
	`78`	`+`
	`79`	`+ build_max_heap(nums, numsSize);`
	`80`	`+`
	`81`	`+ /* nums[0] is the largest element and the last is the least */`
	`82`	`+ for (i = numsSize - 1; i >= numsSize - k + 1; i--) {`
	`83`	`+ swap(&nums[0], &nums[i]);`
	`84`	`+ max_heapify(nums, numsSize, 0);`
	`85`	`+ }`
	`86`	`+`
	`87`	`+ return nums[0];`
	`88`	`+#endif`
`45`	`89`	`}`
`46`	`90`
`47`	`91`

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`‎0215_kth_largest_element_in_an_array/kth_elem.c‎`

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