How to get all subarrays from an array by using JavaScript All In One

JavaScript 动态生成其所有的子数组算法

difficulty: Medium / 难度: 中等

errorrs

two pointers

function getAllSubArrays(arr, start, end, result) {
  if (end === arr.length) {
    return result;
  } else if (start > end) {
    // Increment the end point and start from 0 
    getAllSubArrays(arr, 0, end + 1, result);
  } else {
    // Print the subarray and increment the starting point 
    let temp = [];
    for(let i = start; i < end; i++) {
      temp.push(arr[i]);
    }
    // 丢失 子数组 bug ❌
    // temp.push(arr[end]);
    let str = temp.join(',');
    // let str = temp.join('');
    // 去重 bug ❌ & 去空
    if(!result.includes(str) && temp.length) {
      result.push(str);
    }
    console.log(`subArray =`, temp);
    getAllSubArrays(arr, start + 1, end, result);
  }
  return result;
}
// test
// getAllSubArrays([1,1,2,1,1], 0, 0, [])
// ['1', '1,1', '1,1,2', '1,2', '2', '1,1,2,1', '1,2,1', '2,1']

getAllSubArrays([1,1,2,1,1], 0, 0, []).map(str => str.split(`,`));
// getAllSubArrays([1,1,2,1,1], 0, 0, []).map(str => [...str]);


function getAllSubArrays(arr, start, end, result) {
  if (end === arr.length) {
    return result;
  } else if (start > end) {
    // Increment the end point and start from 0 
    getAllSubArrays(arr, 0, end + 1, result);
  } else {
    let temp = [];
    for(let i = start; i < end; i++) {
      temp.push(arr[i]);
    }
    // ✅ 丢失 子数组  bug fixed
    temp.push(arr[end]);
    let str = temp.join(',');
    // let str = temp.join('');
    // 去重 bug ❌ & 去空
    if(!result.includes(str) && temp.length) {
      result.push(str);
    }
    console.log(`subArray =`, temp);
    getAllSubArrays(arr, start + 1, end, result);
  }
  return result;
}
// test
// getAllSubArrays([1,1,2,1,1], 0, 0, [])
// ['1', '1,1', '1,1,2', '1,2', '2', '1,1,2,1', '1,2,1', '2,1', '1,1,2,1,1', '1,2,1,1', '2,1,1']

// getAllSubArrays([1,1,2,1,1], 0, 0, []).map(str => str.split(`,`));
getAllSubArrays([1,1,2,1,1], 0, 0, []).map(str => str.split(`,`)).map(arr => arr.map(Number));
// getAllSubArrays([1,1,2,1,1], 0, 0, []).map(str => [...str]);
// getAllSubArrays([1,1,2,1,1], 0, 0, []).map(str => [...str]).map(arr => arr.map(Number));

bugs


function numberOfSubarrays(nums: number[], k: number): number {
  let count = 0;
  // sub-arrays 
  // const subarrays = getAllSubarrays(nums);
  const subarrays = getAllSubArrays(nums, 0, 0, []);
  // const subarrays = getAllSubArrays(nums, 0, 0, []).map(str => str.split(`,`));
  // const subarrays = getAllSubArrays([1,1,2,1,1], 0, 0, []).map(str => str.split(`,`)).map(arr => arr.map(Number))
  console.log(`subarrays =`, subarrays)
  for(let subarray of subarrays) {
    // error TS2362: The left-hand side of an arithmetic operation must be of type 'any', 'number', 'bigint' or an enum type.
    // 算术运算的左侧必须是“any”、“number”、“bigint”或枚举类型。
    // let odds = subarray.filter(i => i % 2 !== 0);
    // let odds = subarray.map(Number).filter(i => i % 2 !== 0);
    // 不去重 子数组变多， 导致重复计数 bug ❌ 💩
    let odds = subarray.filter(i => i % 2 !== 0);
    if(odds.length === k) {
      count++;
    }
  }
  return count;
};


// 双指针 ✅
// function getAllSubArrays(arr:number[] = [], start:number = 0, end:number = 0, result:string[] = []) {
function getAllSubArrays(arr:number[] = [], start:number = 0, end:number = 0, result:number[][] = []) {
  if (end === arr.length) {
    return result;
  } else if (start > end) {
    // Increment the end point and start from 0 
    getAllSubArrays(arr, 0, end + 1, result);
  } else {
    // Print the subarray and increment the starting point 
    let temp:number[] = [];
    for(let i = start; i < end; i++) {
      temp.push(arr[i]);
    }
    // let str = temp.join(',');
    // // let str = temp.join('');
    // // 去重 丢失 子数组 bug ❌ & 去空
    // if(!result.includes(str) && temp.length) {
    //   result.push(str);
    //   // console.log(`subArray =`, temp);
    // }
    // 去空 ✅
    if(temp.length) {
      result.push(temp);
      // console.log(`subArray =`, temp);
    }
    getAllSubArrays(arr, start + 1, end, result);
  }
  return result;
}
// function getAllSubarrays(arr: number[], left: number, right: number): number[][] {
//   let result: number[][] = [];
//   while(left <= arr.length - 1) {
//     result.push(arr.slice(left, right));
//     left++;
//   }
//   left = 0;
//   right = arr.length - 1;
//   while(right >= 0) {
//     result.push(arr.slice(left, right));
//     right--;
//   }
//   console.log(`result =`, result);
//   return result;
// };

// 滑动 ❌
// function getAllSubarrays(arr: number[]): number[][] {
//   let result: number[][] = [];
//   let len = arr.length;
//   while(len) {
//     let temp = [];
//     let step = arr.length - len + 1;
//     console.log(`❓ step =`, step)
//     for(let i = 0; i <= arr.length; i++) {
//       if(arr[step]) {
//         temp.push(arr.slice(i, step));
//         result.push(temp);
//       }
//       step++;
//     }
//     console.log(`❌ result =`, result);
//     len--;
//   }
//   console.log(`result =`, result);
//   return result;
// };

// 递归: 排列组合 permutation & composition
// function getAllPermutation(arr: number[]): number[][] {
//   let result: number[][] = [];
//   for(let i = 0; i < arr.length; i++) {
//     let temp = arr[i];
//     let others = getAllPermutation([...arr.slice(0, i), ...arr.slice(i)]);
//     for(let other of others) {
//       result.push([temp, ...other]);
//     }
//   }
//   return result;
// };

solutions

function numberOfSubarrays(nums: number[], k: number): number {
  let len = nums.length;
  let arr = new Array(len + 1).fill(0);
  arr[0] = 1;
  let count = 0;
  let temp = 0;
  for (let num of nums) {
      temp += num & 1;
      if (temp - k >= 0) {
        count += arr[temp - k];
      }
      arr[temp]++;
  }
  return count;
};

two pointers


function getAllSubArrays(arr, start, end, result) {
  if (end === arr.length) {
    return result;
  } else if (start > end) {
    // Increment the end point and start from 0 
    getAllSubArrays(arr, 0, end + 1, result);
  } else {
    let temp = [];
    for(let i = start; i < end; i++) {
      temp.push(arr[i]);
    }
    // ✅ 丢失 子数组  bug fixed
    temp.push(arr[end]);
    // ✅ 去重 bug fixed， 没有必要去空
    // if(temp.length) {
    //   result.push(str);
    // }
     result.push(temp);
    console.log(`subArray =`, temp);
    getAllSubArrays(arr, start + 1, end, result);
  }
  return result;
}
// test ✅
getAllSubArrays([1,1,2,1,1], 0, 0, [])
// [[1],[1,1],[1],[1,1,2],[1,2],[2],[1,1,2,1],[1,2,1],[2,1],[1],[1,1,2,1,1],[1,2,1,1],[2,1,1],[1,1],[1]]

still bug ❓

function numberOfSubarrays(nums: number[], k: number): number {
  let count = 0;
  // sub-arrays 
  const subarrays = getAllSubArrays(nums, 0, 0, []);
  const all_subarrays = getAllSubArrays(nums, 0, 0, []).map(arr => arr.join(`,`));
  console.log(`subarrays =`, all_subarrays)
  for(let subarray of subarrays) {
    let odds = subarray.filter(i => i % 2 !== 0);
    if(odds.length === k) {
      count++;
    }
  }
  return count;
};


// 双指针 ✅
function getAllSubArrays(arr:number[] = [], start:number = 0, end:number = 0, result:number[][] = []) {
  if (end === arr.length) {
    return result;
  } else if (start > end) {
    // Increment the end point and start from 0 
    getAllSubArrays(arr, 0, end + 1, result);
  } else {
    // Print the subarray and increment the starting point 
    let temp:number[] = [];
    for(let i = start; i < end; i++) {
      temp.push(arr[i]);
    }
    // bug fixed ✅
    temp.push(arr[end]);
    // 不需要去重，去空 ✅
    result.push(temp);
    // console.log(`subArray =`, temp);
    getAllSubArrays(arr, start + 1, end, result);
  }
  return result;
}


/* 
Time Limit Exceeded
14 / 38 testcases passed

 */

demos

// 双指针 ???

// function numberOfSubarrays(nums: number[], k: number): number {
//   let count = 0;
//   // sub-arrays 
//   const subarrays = getAllSubarrays(nums);
//   for(let subarray of subarrays) {
//     let odds = subarray.filter(i => i % 2 !== 0);
//     if(odds.length === k) {
//       count++;
//     }
//   }
//   return count;
// };




// 滑动 ❌
// function getAllSubarrays(arr: number[]): number[][] {
//   let result: number[][] = [];
//   let len = arr.length;
//   while(len) {
//     let temp = [];
//     let step = arr.length - len + 1;
//     console.log(`❓ step =`, step)
//     for(let i = 0; i <= arr.length; i++) {
//       if(arr[step]) {
//         temp.push(arr.slice(i, step));
//         result.push(temp);
//       }
//       step++;
//     }
//     console.log(`❌ result =`, result);
//     len--;
//   }
//   console.log(`result =`, result);
//   return result;
// };

// 递归: 排列组合 permutation & composition
// function getAllPermutation(arr: number[]): number[][] {
//   let result: number[][] = [];
//   for(let i = 0; i < arr.length; i++) {
//     let temp = arr[i];
//     let others = getAllPermutation([...arr.slice(0, i), ...arr.slice(i)]);
//     for(let other of others) {
//       result.push([temp, ...other]);
//     }
//   }
//   return result;
// };

https://leetcode.com/problems/count-number-of-nice-subarrays/?envType=daily-question&envId=2024-06-22

(🐞 反爬虫测试！打击盗版⚠️）如果你看到这个信息, 说明这是一篇剽窃的文章，请访问 https://www.cnblogs.com/xgqfrms/ 查看原创文章！

test

// export {};

function printSubArrays(arr, start = 0, end = 0) {
  // Stop if we have reached the end of the array
  if (end === arr.length) {
    return;
  } else if (start > end) {
    // Increment the end point and start from 0 
    printSubArrays(arr, 0, end + 1);
  } else {
    // Print the subarray and increment the starting point 
    let str = `[`;
    for(var i = start; i < end; i++) {
      str += arr[i] + `,`;
    }
    str += arr[end] + `]`;
    console.log(`subArray =`, str);
    printSubArrays(arr, start + 1, end);
  }
  return;
}
// test
let arr = [ 1, 2, 3, 4];
printSubArrays(arr, 0, 0);

// subArray = [1]
// subArray = [1,2]
// subArray = [2]
// subArray = [1,2,3]
// subArray = [2,3]
// subArray = [3]
// subArray = [1,2,3,4]
// subArray = [2,3,4]
// subArray = [3,4]
// subArray = [4]