建议 要比较一下本题和 454.四数相加II 的区别为什么 454.四数相加II 会简单很多这个想明白了对本题理解就深刻了。 本题 思路整体和 三数之和一样的都是双指针但写的时候 有很多小细节需要注意建议先看视频。题目链接https://leetcode.cn/problems/4sum/视频讲解https://www.bilibili.com/video/BV1DS4y147US今日收获这题难度还是有的要细细理解思路理解很关键代码写起来并不简单很多细节需要注意很有挑战性的题目真的很难理解题意非常重要加油intcomp(constvoid*a,constvoid*b){return*(int*)a-*(int*)b;}int**fourSum(int*nums,intnumsSize,inttarget,int*returnSize,int**returnColumnSizes){int**quadrupletsmalloc(sizeof(int*)*1001);*returnSize0;*returnColumnSizesmalloc(sizeof(int)*1001);if(numsSize4)returnquadruplets;qsort(nums,numsSize,sizeof(int),comp);intlengthnumsSize;for(inti0;ilength-3;i){if(i0nums[i]nums[i-1])continue;if((long)nums[i]nums[i1]nums[i2]nums[i3]target)break;if((long)nums[i]nums[length-3]nums[length-2]nums[length-1]target)continue;for(intji1;jlength-2;j){if(ji1nums[j]nums[j-1])continue;if((long)nums[i]nums[j]nums[j1]nums[j2]target)break;if((long)nums[i]nums[j]nums[length-2]nums[length-1]target)continue;intleftj1,rightlength-1;while(leftright){longsum(long)nums[i]nums[j]nums[left]nums[right];if(sumtarget){int*tmpmalloc(sizeof(int)*4);tmp[0]nums[i],tmp[1]nums[j],tmp[2]nums[left],tmp[3]nums[right];(*returnColumnSizes)[(*returnSize)]4;quadruplets[(*returnSize)]tmp;while(leftrightnums[left]nums[left1])left;left;while(leftrightnums[right]nums[right-1])right--;right--;}elseif(sumtarget)left;elseright--;}}}returnquadruplets;}