常见的算法
Posted wangliang2015
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/* 快速排序
* 升序排列
*/
- (void)quickSortArray: (NSArray *)array withLeftIndex: (NSInteger)leftIndex andRightIndex: (NSInteger)rightIndex {
NSMutableArray *arr = [NSMutableArray arrayWithArray:array];
if (leftIndex >= rightIndex) {
return;
}
NSInteger i = leftIndex;
NSInteger j = rightIndex;
NSInteger key = [arr[leftIndex] integerValue];
while (i < j) {
while (i < j && key >= [arr[j] integerValue]) {
j--;
}
arr[i] = arr[j];
while (i < j && key <= [arr[i] integerValue]) {
i++;
}
arr[j] = arr[i];
}
arr[i] = @(key);
[self quickSortArray:arr withLeftIndex:leftIndex andRightIndex:i - 1];
[self quickSortArray:arr withLeftIndex:i + 1 andRightIndex:rightIndex];
}
/* 冒泡排序
* 倒序排列
* 时间复杂度 O(n^2)
*/
- (NSArray *)sortArrayWithDesc: (NSArray *)array {
NSMutableArray *arr = [NSMutableArray arrayWithArray:array];
for (int i = 0; i < arr.count - 1; i++) {
for (int j = 0; j < arr.count - i - 1; j++) {
if (arr[j] < arr[j+1]) {
NSNumber *temp = arr[j];
arr[j] = arr[j+1];
arr[j+1] = temp;
}
}
}
return (NSArray *)arr;
}
/* 选择排序
* 升序排列
*/
- (NSArray *)sortArrayWithAsc: (NSArray *)array {
NSMutableArray *arr = [NSMutableArray arrayWithArray:array];
for (NSInteger i = 0; i < arr.count - 1; i++) {
NSInteger index = 0;
index = i;
for (NSInteger j = i + 1; j < arr.count; j++) {
if (arr[index] > arr[j]) {
index = j;
}
}
if (index != i) {
NSNumber *temp = arr[i];
arr[i] = arr[index];
arr[index] = temp;
}
}
return (NSArray *)arr;
}
/* 从排好序的数组中去重
* 时间复杂度O(n), 空间复杂度O(1)
*/
- (NSInteger)removeDuplicatesFromSortedArray: (NSArray *)nums {
if (nums.count <= 0) return 0;
NSInteger index = 0;
NSMutableArray *temp = [NSMutableArray arrayWithArray:nums];
for (NSInteger i = 1; i < temp.count; i++) {
if (temp[index] != temp[i]) {
temp[++index] = temp[i];
}
}
NSRange range = NSMakeRange(index, nums.count - index - 1);
[temp removeObjectsInRange:range];
NSLog(@"temp===%@", temp);
return index + 1;
}
/* 从排好序的数组中去重,重复最多出现n次
* 时间复杂度O(n), 空间复杂度O(1)
*/
- (NSInteger)removeDuplicatesFromSortedArray: (NSArray *)nums MostDuplicatesCount: (NSInteger)times {
if (nums.count <= times) return nums.count;
NSInteger index = times;
NSMutableArray *temp = [NSMutableArray arrayWithArray:nums];
for (NSInteger i = 1; i < temp.count; i++) {
if (temp[i] != temp[index - times]) {
temp[index++] = temp[i];
}
}
NSRange range = NSMakeRange(index, nums.count - index);
[temp removeObjectsInRange:range];
NSLog(@"temp===%@", temp);
return index;
}
/* 数组无重复,从数组中找到target的位置
* 时间复杂度O(log n), 空间复杂度O(1)
*/
- (NSInteger)searchInRotatedSortedArray: (NSArray *)nums withTarget: (NSNumber *)target {
NSInteger first = 0;
NSInteger last = nums.count;
while (first != last) {
NSInteger mid = first + (last - first) / 2 ;
if (nums[mid] == target) {
return mid;
}
if (nums[first] <= nums[mid]) {
if (nums[first] <= target && target < nums[mid]) {
last = mid;
} else {
first = mid + 1;
}
}
else {
if (nums[mid] < target && target <= nums[last-1]) {
first = mid + 1;
} else {
last = mid;
}
}
}
return -1;
}
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