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解析： 

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代码设计： 

 

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代码： 

写法一：path为全局变量

private int ret,path,aim;public int findTargetSumWays(int[] nums, int target) {aim = target;dfs(nums,0);return ret;}private void dfs(int[] nums, int pos){if(pos == nums.length){if(path == aim) ret++;return;} //添加 '+'path += nums[pos];dfs(nums,pos+1);path -= nums[pos];//回溯//添加 '-'path -= nums[pos];dfs(nums,pos+1); path += nums[pos];//回溯}

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写法二：path作为参数

private int ret,aim;public int findTargetSumWays(int[] nums, int target) {aim = target;dfs(nums,0,0);return ret;}private void dfs(int[] nums, int pos,int path){if(pos == nums.length){if(path == aim) ret++;return;}//添加 '+'dfs(nums, pos+1, path + nums[pos]);//添加 '-'dfs(nums, pos+1, path - nums[pos]); }