2757-GenerateCircularArrayValues.js

// 2757. Generate Circular Array Values
// Given a circular array arr and an integer startIndex, return a generator object gen that yields values from arr. 
// The first time gen.next() is called on the generator, it should should yield arr[startIndex]. Each subsequent time gen.next() is called, an integer jump will be passed into the function (Ex: gen.next(-3)).
//         If jump is positive, the index should increase by that value, however if the current index is the last index, it should instead jump to the first index.
//         If jump is negative, the index should decrease by the magnitude of that value, however if the current index is the first index, it should instead jump to the last index.

// Example 1:
// Input: arr = [1,2,3,4,5], steps = [1,2,6], startIndex = 0
// Output: [1,2,4,5]
// Explanation:  
//  const gen = cycleGenerator(arr, startIndex);
//  gen.next().value;  // 1, index = startIndex = 0
//  gen.next(1).value; // 2, index = 1, 0 -> 1
//  gen.next(2).value; // 4, index = 3, 1 -> 2 -> 3
//  gen.next(6).value; // 5, index = 4, 3 -> 4 -> 0 -> 1 -> 2 -> 3 -> 4

// Example 2:
// Input: arr = [10,11,12,13,14,15], steps = [1,4,0,-1,-3], startIndex = 1
// Output: [11,12,10,10,15,12]
// Explanation: 
//  const gen = cycleGenerator(arr, startIndex);
//  gen.next().value;   // 11, index = 1
//  gen.next(1).value;  // 12, index = 2
//  gen.next(4).value;  // 10, index = 0
//  gen.next(0).value;  // 10, index = 0
//  gen.next(-1).value; // 15, index = 5
//  gen.next(-3).value; // 12, index = 2

// Example 3:
// Input: arr = [2,4,6,7,8,10], steps = [-4,5,-3,10], startIndex = 3
// Output: [7,10,8,4,10]
// Explanation:  
//  const gen = cycleGenerator(arr, startIndex);
//  gen.next().value   // 7,  index = 3
//  gen.next(-4).value // 10, index = 5
//  gen.next(5).value  // 8,  index = 4
//  gen.next(-3).value // 4,  index = 1  
//  gen.next(10).value // 10, index = 5

// Constraints:
//         1 <= arr.length <= 10^4
//         1 <= steps.length <= 100
//         -10^4 <= steps[i], arr[i] <= 10^4
//         0 <= startIndex < arr.length

/**
 * @param {Array<number>} arr
 * @param {number} startIndex
 * @yields {number}
 */
var cycleGenerator = function* (arr, startIndex) {
    const len = arr.length
    while (true) {
        // const jump = yield arr[startIndex];
        // // 如果 jump 是正数，则索引应该增加该值，但如果当前索引是最后一个索引，则应跳转到第一个索引。
        // // 如果 jump 是负数，则索引应减去该值的绝对值，但如果当前索引是第一个索引，则应跳转到最后一个索引。
        // // % len 就是为了保证 [0 - length -1] 之间
        // startIndex = ((startIndex + jump) % len + len) % len;

        // let index = startIndex % len;
        // index = index < 0 ? index + len : index;
        // const jump = yield arr[index];
        // startIndex += jump;

        startIndex %= len
        // 为负数 加上长度
        if (startIndex < 0) startIndex += len
        const jump = yield arr[startIndex]
        startIndex += jump
    }
};

/**
 *  const gen = cycleGenerator([1,2,3,4,5], 0);
 *  gen.next().value  // 1
 *  gen.next(1).value // 2
 *  gen.next(2).value // 4
 *  gen.next(6).value // 5
 */

// Example 1:
console.log("Example 1:");
let gen = cycleGenerator([1,2,3,4,5], 0);
console.log(gen.next().value);  // 1 index = startIndex = 0
console.log(gen.next(1).value); // 2 index = 1, 0 -> 1
console.log(gen.next(2).value); // 4 index = 3, 1 -> 2 -> 3
console.log(gen.next(6).value); // 5 index = 4, 3 -> 4 -> 0 -> 1 -> 2 -> 3 -> 4

// Example 2:
console.log("Example 2:");
gen = cycleGenerator([10,11,12,13,14,15], 1);
console.log(gen.next().value);   // 11, index = 1
console.log(gen.next(1).value);  // 12, index = 2
console.log(gen.next(4).value);  // 10, index = 0
console.log(gen.next(0).value);  // 10, index = 0
console.log(gen.next(-1).value); // 15, index = 5
console.log(gen.next(-3).value); // 12, index = 2

// Example 3:
console.log("Example 3:");
gen = cycleGenerator([2,4,6,7,8,10], 3);
console.log(gen.next().value);   // 7,  index = 3
console.log(gen.next(-4).value); // 10, index = 5
console.log(gen.next(5).value);  // 8,  index = 4
console.log(gen.next(-3).value); // 4,  index = 1  
console.log(gen.next(10).value); // 10, index = 5