## Algorithm

Problem Name: 228. Summary Ranges

You are given a sorted unique integer array nums.

A range [a,b] is the set of all integers from a to b (inclusive).

Return the smallest sorted list of ranges that cover all the numbers in the array exactly. That is, each element of nums is covered by exactly one of the ranges, and there is no integer x such that x is in one of the ranges but not in nums.

Each range [a,b] in the list should be output as:

• "a->b" if a != b
• "a" if a == b

Example 1:

Input: nums = [0,1,2,4,5,7]
Output: ["0->2","4->5","7"]
Explanation: The ranges are:
[0,2] --> "0->2"
[4,5] --> "4->5"
[7,7] --> "7"

Example 2:

Input: nums = [0,2,3,4,6,8,9]
Output: ["0","2->4","6","8->9"]
Explanation: The ranges are:
[0,0] --> "0"
[2,4] --> "2->4"
[6,6] --> "6"
[8,9] --> "8->9"

Constraints:

• 0 <= nums.length <= 20
• -231 <= nums[i] <= 231 - 1
• All the values of nums are unique.
• nums is sorted in ascending order.

## Code Examples

### #1 Code Example with C Programming

Code - C Programming

void ranges(int *nums, int numsz, int ***pp, int *sz, int *n) {
int a, b;
int i, l;
char buff[64];

if (numsz == 0) return;

if (*n == *sz) {
(*sz) *= 2;
(*pp) = realloc(*pp, (*sz) * sizeof(char *));
//assert(*pp);
}
b = a = nums[0];
i = 1;
while (i  <  numsz && (b + 1) == nums[i]) {
i ++; b ++;
}
l = sprintf(buff, "%d", a);
if (i > 1) {
l += sprintf(&buff[l], "->%d", b);
}

(*pp)[*n] = malloc((l + 1) * sizeof(char));
strcpy((*pp)[*n], buff);
(*n) ++;

ranges(&nums[i], numsz - i, pp, sz, n);
}
char** summaryRanges(int* nums, int numsSize, int* returnSize) {
int sz, n;
char **p;

*returnSize = 0;
if (numsSize == 0) return NULL;

sz = 100;
p = malloc(sz * sizeof(char *));

n = 0;
ranges(nums, numsSize, &p, &sz, &n);

*returnSize = n;

return p;
}
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Input

cmd
nums = [0,1,2,4,5,7]

Output

cmd
["0->2","4->5","7"]

### #2 Code Example with C++ Programming

Code - C++ Programming

class Solution {
public:
vector<string> summaryRanges(vector<int>& nums) {
vector < string>res;
for(int i = 0, j = 1; i  <  nums.size(); i = j, j = i + 1){
while(j < nums.size() && nums[j] == nums[j - 1] + 1) j++;
res.push_back((j == i + 1) ? to_string(nums[i]) : to_string(nums[i]) + "->" + to_string(nums[j - 1]));
}
return res;
}
};
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Input

cmd
nums = [0,1,2,4,5,7]

Output

cmd
["0->2","4->5","7"]

### #3 Code Example with Java Programming

Code - Java Programming

class Solution {
public List summaryRanges(int[] nums) {
List result = new ArrayList<>();
int idx = 0;
int n = nums.length;
while (idx  <  n) {
int start = nums[idx];
int end = start;
idx++;
while (idx  <  n && nums[idx] == end + 1) {
end = nums[idx];
idx++;
}
result.add(start == end ? String.valueOf(start) : (start + "->" + end));
}
return result;
}
}
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Input

cmd
nums = [0,2,3,4,6,8,9]

Output

cmd
["0","2->4","6","8->9"]

### #4 Code Example with Javascript Programming

Code - Javascript Programming

const summaryRanges = function(nums) {
if (nums == null || nums.length === 0) return []
const res = []
if (nums.length === 1) return [`\${nums[0]}`]
let start = nums[0]
let end = nums[0]
let endVal = end
for (let i = 1, len = nums.length; i  <  len; i++) {
let cur = nums[i]
if (cur - end > 1) {
endVal = end
insert(res, start, end)
start = cur
end = cur
} else {
end = cur
}
}
if (endVal !== end) {
insert(res, start, end)
}
return res
}

function insert(arr, start, end) {
if (start === end) {
arr.push(`\${start}`)
} else {
arr.push(`\${start}->\${end}`)
}
}
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Input

cmd
nums = [0,2,3,4,6,8,9]

Output

cmd
["0","2->4","6","8->9"]

### #5 Code Example with Python Programming

Code - Python Programming

class Solution:
def summaryRanges(self, nums):
"""
:type nums: List[int]
:rtype: List[str]
"""
res, stack = [], [nums[0] if nums else None, None]
for i, num in enumerate(nums):
if i > 0 and nums[i - 1] == num - 1: stack[1] = num
if i > 0 and nums[i-1] != num - 1: res, stack[0], stack[1] = res + ["->".join(str(q) for q in stack if q != None)], num, None
if i == len(nums) - 1: res.append("->".join(str(q) for q in stack if q != None))
return res
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Input

cmd
nums = [0,1,2,4,5,7]

Output

cmd
["0->2","4->5","7"]