JavaScript 从浅入深 100 题训练计划--(23)最大子数组和（Kadane 算法）

**题目**：给定一个整数数组，找出和最大的连续子数组

maxSubArray([-2,1,-3,4,-1,2,1,-5,4]) // 6 (子数组 [4,-1,2,1])

 

function maxSubArray(nums) {
  let maxSoFar = nums[0];  // 迄今为止的最大值
  let maxEndingHere = nums[0];  // 以当前位置结尾的最大值
  
  for (let i = 1; i < nums.length; i++) {
    // 状态转移：要么扩展之前的子数组，要么从当前元素重新开始
    maxEndingHere = Math.max(nums[i], maxEndingHere + nums[i]);
    maxSoFar = Math.max(maxSoFar, maxEndingHere);
  }
  
  return maxSoFar;
}

// 更简洁的写法
function maxSubArray(nums) {
  let maxSum = nums[0];
  let currentSum = nums[0];
  
  for (let i = 1; i < nums.length; i++) {
    currentSum = Math.max(nums[i], currentSum + nums[i]);
    maxSum = Math.max(maxSum, currentSum);
  }
  
  return maxSum;
}



function maxSubArrayWithIndices(nums) {
  let maxSum = nums[0];
  let currentSum = nums[0];
  let start = 0, end = 0, tempStart = 0;
  
  for (let i = 1; i < nums.length; i++) {
    if (nums[i] > currentSum + nums[i]) {
      currentSum = nums[i];
      tempStart = i;
    } else {
      currentSum = currentSum + nums[i];
    }
    
    if (currentSum > maxSum) {
      maxSum = currentSum;
      start = tempStart;
      end = i;
    }
  }
  
  return {
    maxSum,
    startIndex: start,
    endIndex: end,
    subarray: nums.slice(start, end + 1)
  };
}